Chemistry PYQ Multiple Choice Questions

Class 12 Chemistry Previous Year Questions (MCQs)

1. Which of the following cells has a constant voltage throughout its life?
  • (A) Dry cell
  • (B) Daniell cell
  • (C) Electrolytic cell
  • (D) Mercury cell
Correct Answer: (D) Mercury cell
2. For the reaction \(A + 2B \rightarrow 3C + D\), the rate expression \(\frac{d[C]}{dt}\) is equal to:
  • (A) \(-\frac{d[B]}{dt}\)
  • (B) \(-\frac{3}{2}\frac{d[B]}{dt}\)
  • (C) \(-\frac{d[A]}{dt}\)
  • (D) \(+3\frac{d[A]}{dt}\)
Correct Answer: (B) \(-\frac{3}{2}\frac{d[B]}{dt}\)
3. Which of the following transition metals shows maximum number of oxidation states?
  • (A) Mn
  • (B) Ti
  • (C) Sc
  • (D) Cu
Correct Answer: (A) Mn
4. The secondary valence of Co in \([\text{Co}(\text{NH}_3)_6]\text{Cl}_3\) is:
  • (A) 3
  • (B) 6
  • (C) 5
  • (D) 9
Correct Answer: (B) 6
5. The action of \(\text{HNO}_2\) on methylamine gives mainly:
  • (A) Methyl nitrite
  • (B) Nitromethane
  • (C) Methane
  • (D) Methyl alcohol
Correct Answer: (D) Methyl alcohol
6. The Gabriel phthalimide synthesis is used for the preparation of:
  • (A) Secondary amine
  • (B) Primary aliphatic amines
  • (C) Primary aromatic amines
  • (D) Tertiary amines
Correct Answer: (B) Primary aliphatic amines
7. The deficiency of which vitamin causes pernicious anaemia?
  • (A) Vitamin \(\text{B}_{12}\)
  • (B) Vitamin \(\text{B}_6\)
  • (C) Vitamin \(\text{B}_1\)
  • (D) Vitamin \(\text{B}_2\)
Correct Answer: (A) Vitamin \(\text{B}_{12}\)
8. The \(\alpha\)-helix structure of proteins is stabilized by:
  • (A) van der Waals forces
  • (B) Hydrogen bonds
  • (C) Disulphide bonds
  • (D) Peptide bonds
Correct Answer: (B) Hydrogen bonds
9. The synthesis of alkyl iodide is best done by:
  • (A) Swarts reaction
  • (B) Wurtz reaction
  • (C) Sandmeyer reaction
  • (D) Finkelstein reaction
Correct Answer: (D) Finkelstein reaction
10. Major product obtained when chlorobenzene reacts with methyl chloride and sodium in the presence of dry ether is:
  • (A) Toluene
  • (B) o-Dichlorobenzene
  • (C) Benzene
  • (D) Methane
Correct Answer: (A) Toluene
11. The colligative property preferred for the determination of molar mass of polymers is:
  • (A) Depression in freezing point
  • (B) Osmotic pressure
  • (C) Relative lowering in vapour pressure
  • (D) Elevation in boiling point
Correct Answer: (B) Osmotic pressure
12. The most common and stable oxidation state of lanthanoids is:
  • (A) +4
  • (B) +2
  • (C) +3
  • (D) +6
Correct Answer: (C) +3
13. Assertion (A): When glucose is added to water, an elevation in boiling point is observed.
Reason (R): The lowering of vapour pressure causes elevation in the boiling point.
  • (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
  • (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
  • (C) Assertion (A) is true, but Reason (R) is false.
  • (D) Assertion (A) is false, but Reason (R) is true.
Correct Answer: (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
14. Assertion (A): Methoxyethane reacts with HI to give ethanol and iodomethane.
Reason (R): Reaction of methoxyethane with HI follows \(S_N1\) mechanism.
  • (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
  • (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
  • (C) Assertion (A) is true, but Reason (R) is false.
  • (D) Assertion (A) is false, but Reason (R) is true.
Correct Answer: (C) Assertion (A) is true, but Reason (R) is false. (It follows \(S_N2\) mechanism)
15. Assertion (A): All collisions of reactant molecules lead to product formation.
Reason (R): Only those collisions in which molecules have proper orientation and sufficient kinetic energy (threshold energy) lead to product formation.
  • (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
  • (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
  • (C) Assertion (A) is true, but Reason (R) is false.
  • (D) Assertion (A) is false, but Reason (R) is true.
Correct Answer: (D) Assertion (A) is false, but Reason (R) is true.
16. Assertion (A): AgCN reacts with methyl chloride to give methyl cyanide.
Reason (R): \(\text{CN}^-\) is an ambident nucleophile.
  • (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
  • (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
  • (C) Assertion (A) is true, but Reason (R) is false.
  • (D) Assertion (A) is false, but Reason (R) is true.
Correct Answer: (D) Assertion (A) is false (it forms methyl isocyanide), but Reason (R) is true.