Class 12 Chemistry Previous Year Questions (MCQs)
1. Which of the following cells has a constant voltage throughout its life?
Correct Answer: (D) Mercury cell[span_0](start_span)[span_0](end_span)
2. For the reaction \(A + 2B \rightarrow 3C + D\), the rate expression \(\frac{d[C]}{dt}\) is equal to:
Correct Answer: (B) \(-\frac{3}{2}\frac{d[B]}{dt}\)[span_1](start_span)[span_1](end_span)
3. Which of the following transition metals shows maximum number of oxidation states?
Correct Answer: (A) Mn[span_2](start_span)[span_2](end_span)
4. The secondary valence of Co in \([\text{Co}(\text{NH}_3)_6]\text{Cl}_3\) is:
Correct Answer: (B) 6[span_3](start_span)[span_3](end_span)
5. The action of \(\text{HNO}_2\) on methylamine gives mainly:
Correct Answer: (D) Methyl alcohol[span_4](start_span)[span_4](end_span)
6. The Gabriel phthalimide synthesis is used for the preparation of:
Correct Answer: (B) Primary aliphatic amines[span_5](start_span)[span_5](end_span)
7. The deficiency of which vitamin causes pernicious anaemia?
Correct Answer: (A) Vitamin \(\text{B}_{12}\)[span_6](start_span)[span_6](end_span)
8. The \(\alpha\)-helix structure of proteins is stabilized by:
Correct Answer: (B) Hydrogen bonds[span_7](start_span)[span_7](end_span)
9. The synthesis of alkyl iodide is best done by:
Correct Answer: (D) Finkelstein reaction[span_8](start_span)[span_8](end_span)
10. Major product obtained when chlorobenzene reacts with methyl chloride and sodium in the presence of dry ether is:
Correct Answer: (A) Toluene[span_9](start_span)[span_9](end_span)
11. The colligative property preferred for the determination of molar mass of polymers is:
Correct Answer: (B) Osmotic pressure[span_10](start_span)[span_10](end_span)
12. The most common and stable oxidation state of lanthanoids is:
Correct Answer: (C) +3[span_11](start_span)[span_11](end_span)
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.
Reason (R): The lowering of vapour pressure causes elevation in the boiling point.
Correct Answer: (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).[span_12](start_span)[span_12](end_span)
14. Assertion (A): Methoxyethane reacts with HI to give ethanol and iodomethane.
Reason (R): Reaction of methoxyethane with HI follows \(S_N1\) mechanism.
Reason (R): Reaction of methoxyethane with HI follows \(S_N1\) mechanism.
Correct Answer: (C) Assertion (A) is true, but Reason (R) is false. (It follows \(S_N2\) mechanism)[span_13](start_span)[span_13](end_span)
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.
Reason (R): Only those collisions in which molecules have proper orientation and sufficient kinetic energy (threshold energy) lead to product formation.
Correct Answer: (D) Assertion (A) is false, but Reason (R) is true.[span_14](start_span)[span_14](end_span)
16. Assertion (A): AgCN reacts with methyl chloride to give methyl cyanide.
Reason (R): \(\text{CN}^-\) is an ambident nucleophile.
Reason (R): \(\text{CN}^-\) is an ambident nucleophile.
Correct Answer: (D) Assertion (A) is false (it forms methyl isocyanide), but Reason (R) is true.[span_15](start_span)[span_15](end_span)
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