80 marks · 3 hours · 43 questions · NIOS board pattern · Questions from lesson notes
Full syllabus · Physical & inorganic
43 Q · 80 marks
Full syllabus · Organic chemistry
43 Q · 80 marks
Full syllabus · Biomolecules & everyday chemistry
43 Q · 80 marks
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Q1. How many moles are in 36 g of H2O? (M = 18 g·mol−1)
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: n = m/M = 36/18 = 2 mol.
Q2. The principal quantum number n determines primarily:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: n = shell/energy level; higher n → larger orbital, higher energy.
Q3. The bond angle in a water molecule is approximately:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: H2O is bent (~104.5°) due to two lone pairs on oxygen.
Q4. For ideal solutions, Raoult's law states that partial vapour pressure of a component is:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Pi = xi Pi° — partial pressure proportional to mole fraction.
Q5. For an isolated system, the first law of thermodynamics implies:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Isolated: no heat or work exchange → ΔU = 0.
Q6. The pH of 0.01 M HCl (complete dissociation) is:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: pH = −log(0.01) = 2.
Q7. In a galvanic cell, oxidation occurs at the:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Anode = oxidation; cathode = reduction.
Q8. Which is the most basic oxide?
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Na2O is a strongly basic oxide of an alkali metal.
Q9. Down a group in the p-block, ionisation energy generally:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Atomic size increases down the group → IE generally decreases.
Q10. Ammonia is prepared in the laboratory by heating:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: NH4Cl + NaOH → NH3 + NaCl + H2O (heat).
Q11. The strongest oxidising halogen is:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: F2 is the strongest oxidising agent among halogens.
Q12. Colour of many transition-metal ions is mainly due to:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Partially filled d orbitals allow d–d electronic transitions.
Q13. In [Co(NH3)6]3+, the coordination number of cobalt is:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Six NH3 ligands → coordination number 6.
Q14. IUPAC name of CH3CH2OH is:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Two carbons with OH → ethanol.
Q15. Markovnikov addition of HBr to propene mainly gives:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: H attaches to carbon with more hydrogens → 2-bromopropane.
Q16. SN1 reaction is favoured by:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Tertiary RX form stable carbocations → SN1 favoured.
Q17. State the Lucas test observation for a tertiary alcohol. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Lucas reagent (conc. HCl + anhyd. ZnCl2): tertiary alcohol gives immediate turbidity due to rapid formation of alkyl chloride.
Q18. What is Tollen's reagent test used for? State the observation. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Tollen's reagent [Ag(NH3)2]+ oxidises aldehydes; Ag+ reduced to metallic silver — silver mirror on the tube.
Q19. Write the Hofmann bromamide conversion of an amide in words (carbon count). (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Amide RCONH2 + Br2 + KOH → amine RNH2 with one carbon less than the amide (Hofmann bromamide).
Q20. Define a peptide bond. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Peptide bond is an amide –CO–NH– link formed between the carboxyl group of one α-amino acid and the amino group of another, with loss of water.
Q21. Define saponification. Name the two products from a triglyceride. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Saponification is alkaline hydrolysis of fats/oils: triglyceride + NaOH → soap (RCOONa) + glycerol.
Q22. Calculate molarity of a solution containing 0.25 mol solute in 500 mL solution. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: M = n/V(L) = 0.25/0.5 = 0.50 M.
Q23. State one colligative property of dilute solutions. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Colligative properties depend on number of solute particles: e.g. relative lowering of vapour pressure, elevation of boiling point, depression of freezing point, osmotic pressure.
Q24. Define enthalpy of formation. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Enthalpy of formation is the heat change when one mole of a compound is formed from its elements in their standard states.
Q25. What is a buffer solution? Give one example. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: A buffer resists pH change on small addition of acid/base. Example: CH3COOH + CH3COONa (acidic buffer).
Q26. State Faraday's first law of electrolysis. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Mass of substance deposited/liberated is proportional to quantity of electricity (charge) passed: m ∝ Q = It.
Q27. What is hybridisation of carbon in ethene? (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Carbon in ethene is sp2 hybridised: three sp2 orbitals form σ bonds in a plane; unhybridised p forms π bond.
Q28. Why is Sc3+ colourless while Ti3+ is coloured in aqueous solution? (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Sc3+ is d0 — no d–d transition. Ti3+ is d1 — can absorb visible light for d–d transition → coloured.
Q29. State Pauli's exclusion principle. (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: No two electrons in an atom can have the same set of four quantum numbers. Thus an orbital holds at most two electrons with opposite spins.
Q30. Why is the atomic radius of N smaller than that of C? (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Across period, nuclear charge increases while electrons add to same shell; stronger attraction pulls shells in — N has higher Z than C → smaller radius.
Q31. Define coordination number and ligand with one example each. (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Coordination number = number of ligand donor atoms bonded to central metal. Ligand = ion/molecule donating electron pair (e.g. NH3 in [Cu(NH3)4]2+; CN = 4).
Q32. State Markovnikov's rule. (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: In addition of HX to unsymmetrical alkene, H attaches to the carbon already having more hydrogens; halogen to the other carbon.
Q33. Why are phenols more acidic than alcohols? (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Phenoxide ion is resonance-stabilised by the aromatic ring; alkoxide is not. Hence phenols are stronger acids than aliphatic alcohols.
Q34. Distinguish aldehydes from ketones using one chemical test. (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Aldehydes give silver mirror with Tollen's (or brick-red Cu2O with Fehling's for aliphatic). Ketones do not under mild conditions.
Q35. Why is aniline a weaker base than ethanamine? (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Lone pair on N in aniline is delocalised into the benzene ring (resonance), less available for protonation; ethanamine lone pair is more available.
Q36. Differentiate DNA and RNA by one structural feature each. (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: DNA: 2-deoxyribose sugar, bases A,G,C,T, usually double helix. RNA: ribose sugar, bases A,G,C,U, usually single strand.
Q37. Why do detergents work better than soaps in hard water? (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Ca2+/Mg2+ form insoluble scum with soaps. Detergent salts with Ca2+/Mg2+ remain water-soluble, so cleaning continues.
Q38. Explain common-ion effect with the example of CH3COOH + CH3COONa. (50–80 words.)
Suggested length: up to 70 words · 3 marks
0 / 70 words
How to approach: Structure: definition/equation (1) → reasoning/working (1) → conclusion/example (1). Use 50–80 words.
NIOS marking: 3 marks = key equation or definition (1) + correct working/reasoning (1) + conclusion or example (1).
Example: Example: SN1: tertiary RX → carbocation → Nu attack; racemisation possible.
Common mistakes: Skipping working; missing keywords; no example where asked.
Model answer: CH3COOH ⇌ H+ + CH3COO−. Adding CH3COONa increases [CH3COO−], shifts equilibrium left (Le Chatelier), suppressing dissociation of acid — common-ion effect. Used in buffers.
Q39. Write the Nernst equation for a general cell reaction and explain each term. (50–80 words.)
Suggested length: up to 70 words · 3 marks
0 / 70 words
How to approach: Structure: definition/equation (1) → reasoning/working (1) → conclusion/example (1). Use 50–80 words.
NIOS marking: 3 marks = key equation or definition (1) + correct working/reasoning (1) + conclusion or example (1).
Example: Example: SN1: tertiary RX → carbocation → Nu attack; racemisation possible.
Common mistakes: Skipping working; missing keywords; no example where asked.
Model answer: E = E° − (RT/nF) ln Q (or 0.059/n log Q at 25 °C). E = cell potential; E° = standard; n = electrons; Q = reaction quotient; R,T,F constants.
Q40. Compare SN1 and SN2 with respect to substrate and kinetics. (50–80 words.)
Suggested length: up to 70 words · 3 marks
0 / 70 words
How to approach: Structure: definition/equation (1) → reasoning/working (1) → conclusion/example (1). Use 50–80 words.
NIOS marking: 3 marks = key equation or definition (1) + correct working/reasoning (1) + conclusion or example (1).
Example: Example: SN1: tertiary RX → carbocation → Nu attack; racemisation possible.
Common mistakes: Skipping working; missing keywords; no example where asked.
Model answer: SN1: unimolecular, rate = k[RX], favoured by 3° RX via carbocation. SN2: bimolecular, rate = k[RX][Nu], favoured by 1° RX; backside attack, inversion.
Q41. Explain bleaching action of chlorine water. (50–80 words.)
Suggested length: up to 70 words · 3 marks
0 / 70 words
How to approach: Structure: definition/equation (1) → reasoning/working (1) → conclusion/example (1). Use 50–80 words.
NIOS marking: 3 marks = key equation or definition (1) + correct working/reasoning (1) + conclusion or example (1).
Example: Example: SN1: tertiary RX → carbocation → Nu attack; racemisation possible.
Common mistakes: Skipping working; missing keywords; no example where asked.
Model answer: Cl2 + H2O ⇌ HCl + HOCl. Nascent oxygen from HOCl oxidises coloured matter to colourless products — bleaching. Permanent in sunlight as HOCl decomposes.
Q42. State the first law of thermodynamics. Explain ΔU = q − w for a system doing work. Give one example of an endothermic process. (80–120 words.)
Suggested length: up to 100 words · 5 marks
0 / 100 words
How to approach: Plan 80–120 words: statement (1) → equations/diagram (1) → explanation with steps (2) → conclusion (1).
NIOS marking: 5 marks = statement (1) + equations/points (1) + detailed explanation (2) + conclusion (1).
Example: Example: State saponification, write fat + NaOH → soap + glycerol, explain micelle cleaning, hard-water limitation.
Common mistakes: Only definition without equations; no structure; missing conclusion; irrelevant material.
Model answer: First law: energy is conserved; ΔU = q − w (school convention: w work by system). Heat absorbed increases U; work done by system decreases U. Example: melting of ice at 0 °C absorbs heat (endothermic).
Q43. Explain cleansing action of soap with the structure of soap molecule and micelles. Why is soap less effective in hard water? (80–120 words.)
Suggested length: up to 100 words · 5 marks
0 / 100 words
How to approach: Plan 80–120 words: statement (1) → equations/diagram (1) → explanation with steps (2) → conclusion (1).
NIOS marking: 5 marks = statement (1) + equations/points (1) + detailed explanation (2) + conclusion (1).
Example: Example: State saponification, write fat + NaOH → soap + glycerol, explain micelle cleaning, hard-water limitation.
Common mistakes: Only definition without equations; no structure; missing conclusion; irrelevant material.
Model answer: Soap has hydrophilic –COO− head and hydrophobic alkyl tail. In water, micelles form with tails inward trapping grease; heads outward keep emulsion soluble — dirt rinses away. Hard water Ca2+/Mg2+ form insoluble scum with soap, reducing lather and cleaning.
Q1. The functional group –CHO indicates:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: –CHO is the aldehyde functional group.
Q2. Ethene on catalytic hydrogenation gives:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: H2/Ni adds across C=C → ethane.
Q3. Aqueous KOH with primary alkyl halide mainly gives:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Nucleophilic substitution → ROH.
Q4. Oxidation of a secondary alcohol mainly gives:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: 2° ROH → ketone on oxidation.
Q5. Aldol condensation requires the carbonyl to have:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: α-H needed for enolate → aldol.
Q6. Carbylamine test is positive for:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: 1° amine + CHCl3/KOH → foul isocyanide.
Q7. Glucose is classified as a:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Glucose is an aldohexose (aldehyde, six carbons).
Q8. Nylon-66 is a:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Hexamethylenediamine + adipic acid → nylon-66 (condensation).
Q9. Avogadro's number is approximately:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: NA ≈ 6.022 × 10^23 mol−1.
Q10. The maximum number of electrons in a shell with principal quantum number n is:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Maximum electrons in shell = 2n².
Q11. Ionic bonds form mainly between:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Large electronegativity difference → electron transfer → ionic bond.
Q12. Molality is defined as:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: m = n_solute / mass_solvent(kg).
Q13. A process with ΔH > 0 and ΔS > 0 is spontaneous at:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: ΔG = ΔH − TΔS; positive ΔS can make ΔG negative at high T.
Q14. For a weak acid HA, Ka is:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Ka = [H+][A−]/[HA].
Q15. Standard hydrogen electrode potential is taken as:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: By definition E°(H+/H2) = 0.00 V.
Q16. EDTA is an example of a:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: EDTA has six donor sites — hexadentate.
Q17. Why does the reactivity of alkali metals increase down the group? (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Atomic size increases and ionisation energy decreases down the group — easier to lose valence electron → higher reactivity.
Q18. State the inert pair effect in one sentence with an example element. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Tendency of ns2 electrons to remain unshared in heavier p-block elements — e.g. Pb prefers +2 over +4.
Q19. Write the products of reaction of NH3 with HCl. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: NH3 + HCl → NH4Cl (ammonium chloride).
Q20. Why is HF a weak acid compared to HCl in water? (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Strong H–F bond and H-bonding in HF hinder complete dissociation; HCl fully ionises — stronger acid.
Q21. Name two characteristic properties of transition metals. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Variable oxidation states; coloured ions/complexes; catalytic activity; formation of complexes (any two).
Q22. Give the IUPAC name of CH3COCH3. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: IUPAC: propan-2-one (common: acetone).
Q23. What is the product of complete hydrogenation of ethyne? (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Ethyne + 2 H2 (Ni/Pt) → ethane.
Q24. State the product of dehydration of ethanol at high temperature with conc. H2SO4. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: At higher temperature, ethanol dehydrates to ethene (intramolecular dehydration).
Q25. What is Cannizzaro reaction? Name one substrate. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Aldehyde without α-H + conc. NaOH → alcohol + salt of acid (disproportionation). Example: HCHO or PhCHO.
Q26. What is diazotisation? State temperature condition. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Conversion of primary aromatic amine to diazonium salt using NaNO2/HCl at 0–5 °C.
Q27. Name the two fractions of starch. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Starch consists of amylose (linear α-glucose) and amylopectin (branched α-glucose).
Q28. Name the monomers of terylene (Dacron). (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Ethylene glycol + terephthalic acid (condensation polyester).
Q29. Define mole. How many molecules are in 1 mole of any substance? (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: One mole contains Avogadro's number of entities (6.022 × 10^23). It is the SI unit of amount of substance.
Q30. Explain why BeH2 is linear while H2S is bent. (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: BeH2: two bonding pairs, no lone pairs → linear. H2S: two bonding + two lone pairs → bent molecular shape.
Q31. State Henry's law. (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: At constant temperature, solubility of a gas in a liquid is proportional to the partial pressure of the gas above the liquid.
Q32. Define pH and write the relation with [H+]. (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: pH = −log10[H+]. Lower pH means higher [H+] (more acidic).
Q33. What is a salt bridge? State one function. (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Tube with electrolyte gel connecting half-cells. Completes circuit and maintains electrical neutrality by ion flow.
Q34. Write the IUPAC name of [Ni(CO)4]. (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Tetracarbonylnickel(0) — four CO ligands, Ni oxidation state 0.
Q35. Why is vinyl chloride unreactive toward SN1/SN2? (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: C–Cl bond has partial double-bond character (resonance with C=C); carbon is sp2 — SN1/SN2 difficult.
Q36. State products of oxidation of ethanal with mild oxidising agents. (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Ethanal oxidises easily to ethanoic acid (acetic acid).
Q37. What is the Hinsberg test used for? (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Distinguishes 1°, 2° and 3° amines using benzenesulphonyl chloride and KOH (solubility pattern of products).
Q38. Explain electrophilic addition of Br2 to ethene with mechanism outline. (50–80 words.)
Suggested length: up to 70 words · 3 marks
0 / 70 words
How to approach: Structure: definition/equation (1) → reasoning/working (1) → conclusion/example (1). Use 50–80 words.
NIOS marking: 3 marks = key equation or definition (1) + correct working/reasoning (1) + conclusion or example (1).
Example: Example: SN1: tertiary RX → carbocation → Nu attack; racemisation possible.
Common mistakes: Skipping working; missing keywords; no example where asked.
Model answer: Br2 polarises; Br+ attacks π bond → cyclic bromonium; Br− opens ring → 1,2-dibromoethane. Electrophilic addition characteristic of alkenes.
Q39. Compare acidity of ethanol and phenol with reason. (50–80 words.)
Suggested length: up to 70 words · 3 marks
0 / 70 words
How to approach: Structure: definition/equation (1) → reasoning/working (1) → conclusion/example (1). Use 50–80 words.
NIOS marking: 3 marks = key equation or definition (1) + correct working/reasoning (1) + conclusion or example (1).
Example: Example: SN1: tertiary RX → carbocation → Nu attack; racemisation possible.
Common mistakes: Skipping working; missing keywords; no example where asked.
Model answer: Phenol (pKa ~10) is more acidic than ethanol (pKa ~16) because phenoxide is resonance-stabilised; ethoxide is not.
Q40. Describe primary and secondary structure of proteins briefly. (50–80 words.)
Suggested length: up to 70 words · 3 marks
0 / 70 words
How to approach: Structure: definition/equation (1) → reasoning/working (1) → conclusion/example (1). Use 50–80 words.
NIOS marking: 3 marks = key equation or definition (1) + correct working/reasoning (1) + conclusion or example (1).
Example: Example: SN1: tertiary RX → carbocation → Nu attack; racemisation possible.
Common mistakes: Skipping working; missing keywords; no example where asked.
Model answer: Primary: amino-acid sequence linked by peptide bonds. Secondary: regular folding via H-bonds — α-helix or β-pleated sheet.
Q41. Differentiate addition and condensation polymerisation with one example each. (50–80 words.)
Suggested length: up to 70 words · 3 marks
0 / 70 words
How to approach: Structure: definition/equation (1) → reasoning/working (1) → conclusion/example (1). Use 50–80 words.
NIOS marking: 3 marks = key equation or definition (1) + correct working/reasoning (1) + conclusion or example (1).
Example: Example: SN1: tertiary RX → carbocation → Nu attack; racemisation possible.
Common mistakes: Skipping working; missing keywords; no example where asked.
Model answer: Addition: unsaturated monomers join without eliminating small molecules (polyethene from ethene). Condensation: bifunctional monomers lose H2O etc. (nylon-66, terylene).
Q42. Explain nucleophilic addition to carbonyl compounds. Why are aldehydes more reactive than ketones? Give one example reaction. (80–120 words.)
Suggested length: up to 100 words · 5 marks
0 / 100 words
How to approach: Plan 80–120 words: statement (1) → equations/diagram (1) → explanation with steps (2) → conclusion (1).
NIOS marking: 5 marks = statement (1) + equations/points (1) + detailed explanation (2) + conclusion (1).
Example: Example: State saponification, write fat + NaOH → soap + glycerol, explain micelle cleaning, hard-water limitation.
Common mistakes: Only definition without equations; no structure; missing conclusion; irrelevant material.
Model answer: C=O is polar (Cδ+); Nu attacks carbon → tetrahedral intermediate. Aldehydes more reactive: less +I (one alkyl) and less steric hindrance than ketones. Example: RCHO + HCN → cyanohydrin.
Q43. Describe preparation of aniline from nitrobenzene and conversion of aniline to chlorobenzene via diazonium salt. (80–120 words.)
Suggested length: up to 100 words · 5 marks
0 / 100 words
How to approach: Plan 80–120 words: statement (1) → equations/diagram (1) → explanation with steps (2) → conclusion (1).
NIOS marking: 5 marks = statement (1) + equations/points (1) + detailed explanation (2) + conclusion (1).
Example: Example: State saponification, write fat + NaOH → soap + glycerol, explain micelle cleaning, hard-water limitation.
Common mistakes: Only definition without equations; no structure; missing conclusion; irrelevant material.
Model answer: Nitrobenzene + Sn/HCl (or Fe/HCl) → aniline. Aniline + NaNO2/HCl at 0–5 °C → PhN2+Cl−; CuCl (Sandmeyer) → chlorobenzene + N2.
Q1. The sugar present in DNA is:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: DNA contains 2-deoxyribose.
Q2. Soap is chemically:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Soap = RCOONa/K from saponification of fats.
Q3. Number of atoms in 0.5 mol of O2 molecules is:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: 0.5 mol O2 has 0.5×NA molecules and 1.0×NA atoms of O.
Q4. Isotopes of an element have the same:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Same Z (protons), different neutron number.
Q5. The shape of methane molecule is:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: sp3 carbon → tetrahedral CH4.
Q6. An azeotrope is a mixture that:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Azeotropes distill unchanged in composition.
Q7. Entropy of the universe in a spontaneous process:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Second law: ΔSuniverse > 0 for spontaneous processes.
Q8. A solution of pH 3 is how many times more acidic (in [H+]) than pH 5?
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: [H+] differs by 10^(5−3) = 100 times.
Q9. The unit of electrochemical equivalent is related to:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Z = m/Q — mass per unit charge.
Q10. Which alkali metal is used in photoelectric cells?
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Low ionisation energy metals (e.g. Cs, K) used in photocells.
Q11. The hybridisation of B in BF3 is:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Trigonal planar BF3 → sp2.
Q12. Oxides of nitrogen that cause acid rain include:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: NOx dissolve to form nitrous/nitric acids.
Q13. Iodine gives blue colour with:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Iodine–starch complex is blue-black.
Q14. The electronic configuration of Cr (Z=24) is exceptional due to:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Cr is 3d5 4s1 — half-filled d stability.
Q15. Homologous series members differ by:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Successive members differ by CH2.
Q16. Benzene undergoes electrophilic substitution rather than addition mainly because:
How to approach: Read all four options. Eliminate wrong units, formulas or definitions. Choose the option matching NIOS notes/PYQ.
NIOS marking: NIOS awards 1 mark all-or-nothing for the correct option. No partial marking in Section A MCQ.
Example: Example: Molarity M = n/V(L); 0.5 mol in 0.25 L → M = 2.0 M (not 0.5 M).
Common mistakes: Confusing similar terms (molarity vs molality; aldose vs ketose; SN1 vs SN2); unit mistakes.
Model answer: Delocalisation energy makes substitution preferred over addition.
Q17. Name the product when CH3Br reacts with alcoholic AgCN (major). (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Alcoholic AgCN mainly gives methyl isocyanide (CH3NC) — isocyanide form preferred with AgCN.
Q18. What is the Williamson synthesis used for? (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Preparation of ethers: alkoxide + primary alkyl halide → ROR′ (SN2).
Q19. Name the product of Rosenmund reduction of an acid chloride. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: RCOCl + H2/Pd-BaSO4 (poisoned) → RCHO (aldehyde).
Q20. Write products of ethanamine with excess CH3I eventually. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Successive alkylation can give tertiary amine and finally quaternary ammonium salt R4N+I−.
Q21. What are essential amino acids? (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Amino acids that cannot be synthesised by the body and must be obtained from diet (~10 of ~20).
Q22. What is vulcanisation of rubber? (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Heating natural rubber with sulphur forms cross-links — improves elasticity, hardness and solvent resistance.
Q23. Calculate number of moles in 11.2 L of O2 at STP (ideal). (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: At STP, 22.4 L = 1 mol; 11.2 L = 0.5 mol O2.
Q24. State Hund's rule of maximum multiplicity. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Electrons occupy degenerate orbitals singly with parallel spins before pairing.
Q25. What is a hydrogen bond? Give one example. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Attractive interaction between H attached to F/O/N and another electronegative atom. Example: H2O, HF, NH3.
Q26. Define osmosis. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Spontaneous flow of solvent through a semipermeable membrane from dilute to concentrated solution.
Q27. Define Gibbs free energy change for spontaneity. (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Process is spontaneous if ΔG < 0 (at constant T, P). ΔG = ΔH − TΔS.
Q28. What is the ionic product of water Kw at 25 °C? (25–35 words.)
Suggested length: up to 30 words · 2 marks
0 / 30 words
How to approach: Answer in 25–35 words. State formula/definition, substitute or explain briefly, give final answer with units where needed.
NIOS marking: 2 marks = correct formula/concept (1) + correct value/explanation (1).
Example: Example: pH = −log[H+] = −log(0.001) = 3 for 0.001 M HCl.
Common mistakes: Formula without value; value without units; vague one-word answers; exceeding word limit.
Model answer: Kw = [H+][OH−] = 1.0 × 10−14 at 25 °C.
Q29. Define standard electrode potential. (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Potential of an electrode relative to SHE when ions are at unit activity (≈1 M) and gases at 1 bar, usually at 25 °C. Often quoted as reduction potential.
Q30. Why is Li different from other alkali metals in some properties? (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Small size and high polarising power of Li+ cause anomalous behaviour (e.g. forms oxide, covalent character) — diagonal relationship with Mg.
Q31. State one difference between diamond and graphite structure. (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Diamond: 3D tetrahedral sp3 network (hard). Graphite: sp2 layers with weak interlayer forces (soft, conducting).
Q32. Write the reaction of NH3 with Cu2+ giving deep blue complex (name/formula). (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Cu2+ + 4 NH3 → [Cu(NH3)4]2+ (deep blue tetraamminecopper(II)).
Q33. Arrange F2, Cl2, Br2, I2 in order of oxidising power. (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Oxidising power: F2 > Cl2 > Br2 > I2.
Q34. Why do transition metals form complexes readily? (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Small size, high charge density and vacant d orbitals allow acceptance of ligand electron pairs → stable complexes.
Q35. What is a chelate? Give one example ligand. (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Complex with ligand forming a ring by binding through two or more donor atoms. Example: en (ethylenediamine), EDTA.
Q36. State Hückel's rule for aromaticity. (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Planar cyclic conjugated system with (4n+2) π electrons (n = 0,1,2…) is aromatic (e.g. benzene n=1, 6π).
Q37. What is the cumene process used for industrially? (30–50 words.)
Suggested length: up to 40 words · 2 marks
0 / 40 words
How to approach: Write 30–50 words. Open with definition/law/name, then one-line explanation or equation.
NIOS marking: 2 marks = correct statement/formula (1) + brief explanation/application (1).
Example: Example: Buffer resists pH change — mixture of weak acid and its salt (common ion).
Common mistakes: Long essay; missing key term; wrong equation; copying notes without answering the question.
Model answer: Industrial manufacture of phenol (and acetone as co-product) from cumene (isopropylbenzene).
Q38. Explain the carbylamine reaction and its use as a test. (50–80 words.)
Suggested length: up to 70 words · 3 marks
0 / 70 words
How to approach: Structure: definition/equation (1) → reasoning/working (1) → conclusion/example (1). Use 50–80 words.
NIOS marking: 3 marks = key equation or definition (1) + correct working/reasoning (1) + conclusion or example (1).
Example: Example: SN1: tertiary RX → carbocation → Nu attack; racemisation possible.
Common mistakes: Skipping working; missing keywords; no example where asked.
Model answer: 1° amine heated with CHCl3 and alc. KOH → isocyanide (foul smell). Used as test for primary amines only.
Q39. Differentiate fat and oil. Mention one biological role of lipids. (50–80 words.)
Suggested length: up to 70 words · 3 marks
0 / 70 words
How to approach: Structure: definition/equation (1) → reasoning/working (1) → conclusion/example (1). Use 50–80 words.
NIOS marking: 3 marks = key equation or definition (1) + correct working/reasoning (1) + conclusion or example (1).
Example: Example: SN1: tertiary RX → carbocation → Nu attack; racemisation possible.
Common mistakes: Skipping working; missing keywords; no example where asked.
Model answer: Fat: solid/semisolid at RT (more saturated). Oil: liquid at RT (more unsaturated). Lipids store energy, form membranes, aid ADEK absorption.
Q40. Derive the relation between Ka and Kb for a conjugate acid–base pair (Kw = Ka×Kb). (50–80 words.)
Suggested length: up to 70 words · 3 marks
0 / 70 words
How to approach: Structure: definition/equation (1) → reasoning/working (1) → conclusion/example (1). Use 50–80 words.
NIOS marking: 3 marks = key equation or definition (1) + correct working/reasoning (1) + conclusion or example (1).
Example: Example: SN1: tertiary RX → carbocation → Nu attack; racemisation possible.
Common mistakes: Skipping working; missing keywords; no example where asked.
Model answer: For HA ⇌ H+ + A−, Ka = [H+][A−]/[HA]. For A− + H2O ⇌ HA + OH−, Kb = [HA][OH−]/[A−]. Multiplying: KaKb = [H+][OH−] = Kw.
Q41. Explain corrosion of iron as an electrochemical process briefly. (50–80 words.)
Suggested length: up to 70 words · 3 marks
0 / 70 words
How to approach: Structure: definition/equation (1) → reasoning/working (1) → conclusion/example (1). Use 50–80 words.
NIOS marking: 3 marks = key equation or definition (1) + correct working/reasoning (1) + conclusion or example (1).
Example: Example: SN1: tertiary RX → carbocation → Nu attack; racemisation possible.
Common mistakes: Skipping working; missing keywords; no example where asked.
Model answer: Anodic: Fe → Fe2+ + 2e−. Cathodic: O2 + 2H2O + 4e− → 4OH−. Fe2+ forms Fe(OH)2/ rust (hydrated Fe2O3). Needs water and oxygen.
Q42. Describe the double-helical structure of DNA. Mention base pairing and one biological function. (80–120 words.)
Suggested length: up to 100 words · 5 marks
0 / 100 words
How to approach: Plan 80–120 words: statement (1) → equations/diagram (1) → explanation with steps (2) → conclusion (1).
NIOS marking: 5 marks = statement (1) + equations/points (1) + detailed explanation (2) + conclusion (1).
Example: Example: State saponification, write fat + NaOH → soap + glycerol, explain micelle cleaning, hard-water limitation.
Common mistakes: Only definition without equations; no structure; missing conclusion; irrelevant material.
Model answer: DNA is a double helix (Watson–Crick): two complementary strands, sugar–phosphate backbone, bases inside. A pairs with T (2 H-bonds), G with C (3 H-bonds). Stores genetic information and templates replication/transcription.
Q43. Compare soaps and detergents under: chemical nature, hard water behaviour, and biodegradability of alkylbenzene sulphonates. (80–120 words.)
Suggested length: up to 100 words · 5 marks
0 / 100 words
How to approach: Plan 80–120 words: statement (1) → equations/diagram (1) → explanation with steps (2) → conclusion (1).
NIOS marking: 5 marks = statement (1) + equations/points (1) + detailed explanation (2) + conclusion (1).
Example: Example: State saponification, write fat + NaOH → soap + glycerol, explain micelle cleaning, hard-water limitation.
Common mistakes: Only definition without equations; no structure; missing conclusion; irrelevant material.
Model answer: Soap: RCOONa from fats. Detergent: alkyl sulphates/sulphonates. Soap fails in hard water (scum); detergents' Ca/Mg salts soluble. Linear ABS ~90% biodegradable; branched ABS poorer (~50–60%) — pollution concern.