CBSE Class 12 Chemistry - 25 Theory PYQ Based MCQ Quiz with answers

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CBSE Class 12 Chemistry – 25 Theory PYQ-Based MCQs

Conceptual questions based on recurring CBSE Class XII Chemistry previous-year question themes.

Theory-focused: no lengthy numerical calculations.

Note: These are PYQ-based/paraphrased practice questions, not verbatim reproduction of CBSE question papers. The 2025–26 official CBSE Chemistry sample paper uses objective questions in Section A and covers the Class XII Chemistry syllabus.

Solutions

1. Which colligative property is used to determine the molar mass of proteins and polymers most conveniently?

(A) Elevation in boiling point(B) Depression in freezing point(C) Osmotic pressure(D) Relative lowering of vapour pressure

Correct Answer: (C) Osmotic pressure

Solutions

2. For a dilute solution, the relative lowering of vapour pressure is equal to the:

(A) Mole fraction of solute(B) Molarity of solvent(C) Mole fraction of solvent(D) Molality of solvent

Correct Answer: (A) Mole fraction of solute

Electrochemistry

3. The standard electrode potential of the standard hydrogen electrode is assigned the value:

(A) 1.00 V(B) 0.00 V(C) -1.00 V(D) 0.059 V

Correct Answer: (B) 0.00 V

Electrochemistry

4. According to Kohlrausch's law, limiting molar conductivity of an electrolyte is:

(A) Independent of ions(B) The sum of contributions of its ions(C) Always zero(D) Equal to its resistance

Correct Answer: (B) The sum of contributions of its ions

Chemical Kinetics

5. For a first-order reaction, the half-life is:

(A) Dependent on initial concentration(B) Independent of initial concentration(C) Always zero(D) Directly proportional to initial concentration

Correct Answer: (B) Independent of initial concentration

Chemical Kinetics

6. The unit of the rate constant for a first-order reaction is:

(A) mol L⁻¹ s⁻¹(B) L mol⁻¹ s⁻¹(C) s⁻¹(D) mol² L⁻² s⁻¹

Correct Answer: (C) s⁻¹

d- and f-Block Elements

7. Which property is commonly associated with transition elements?

(A) Only +1 oxidation state(B) Variable oxidation states(C) Absence of complex formation(D) Always colourless ions

Correct Answer: (B) Variable oxidation states

d- and f-Block Elements

8. Lanthanide contraction refers to the:

(A) Increase in atomic size across lanthanides(B) Gradual decrease in atomic/ionic radii across lanthanides(C) Increase in density only(D) Loss of all 4f electrons

Correct Answer: (B) Gradual decrease in atomic/ionic radii across lanthanides

Coordination Compounds

9. In the coordination compound [Co(NH₃)₆]Cl₃, the coordination number of cobalt is:

(A) 3(B) 4(C) 6(D) 9

Correct Answer: (C) 6

Coordination Compounds

10. The species attached directly to the central metal ion in a coordination compound are called:

(A) Counter ions(B) Ligands(C) Anions only(D) Catalysts

Correct Answer: (B) Ligands

Haloalkanes and Haloarenes

11. Which mechanism is generally favoured by a tertiary alkyl halide with a weak nucleophile in a polar protic medium?

(A) SN1(B) SN2(C) E2 only(D) Free-radical substitution

Correct Answer: (A) SN1

Alcohols, Phenols and Ethers

12. Phenol is more acidic than ethanol mainly because:

(A) Phenol has no oxygen(B) Phenoxide ion is resonance-stabilised(C) Ethanol is aromatic(D) Phenol has fewer hydrogen atoms

Correct Answer: (B) Phenoxide ion is resonance-stabilised

Aldehydes, Ketones and Carboxylic Acids

13. Which reagent is commonly used to distinguish aldehydes from ketones?

(A) Tollens' reagent(B) NaCl solution(C) Dilute HCl only(D) Bromide ion

Correct Answer: (A) Tollens' reagent

Amines

14. Aniline is less basic than ethylamine mainly because:

(A) Aniline contains no nitrogen(B) The lone pair on nitrogen is delocalised into the benzene ring(C) Ethylamine is aromatic(D) Aniline has no lone pair

Correct Answer: (B) The lone pair on nitrogen is delocalised into the benzene ring

Biomolecules

15. The linkage joining two amino acids in a protein is called a:

(A) Glycosidic linkage(B) Peptide linkage(C) Phosphodiester linkage(D) Disulphide linkage only

Correct Answer: (B) Peptide linkage

Biomolecules

16. Which of the following is a reducing sugar?

(A) Sucrose(B) Glucose(C) Starch(D) Cellulose

Correct Answer: (B) Glucose

Amines

17. Diazotisation of a primary aromatic amine is generally carried out at:

(A) 0–5 °C(B) 50–60 °C(C) 100 °C(D) Room temperature only

Correct Answer: (A) 0–5 °C

Haloalkanes and Haloarenes

18. Aryl halides are less reactive towards nucleophilic substitution than alkyl halides mainly due to:

(A) Absence of carbon(B) Resonance and partial double-bond character of C–X(C) Very weak C–X bond(D) Presence of ionic C–X bond

Correct Answer: (B) Resonance and partial double-bond character of C–X

Alcohols, Phenols and Ethers

19. When ethanol is heated with concentrated H₂SO₄ at about 443 K, the major product is:

(A) Ethene(B) Ethane(C) Ethanal(D) Diethyl ether

Correct Answer: (A) Ethene

Aldehydes, Ketones and Carboxylic Acids

20. Aldehydes generally undergo oxidation to form:

(A) Alcohols(B) Carboxylic acids(C) Alkanes(D) Ethers

Correct Answer: (B) Carboxylic acids

Amines

21. The reaction of an amine with nitrous acid can be used to identify:

(A) Primary amines(B) Alkanes(C) Ketones only(D) Carboxylic acids only

Correct Answer: (A) Primary amines

Coordination Compounds

22. The oxidation state of cobalt in [Co(NH₃)₆]Cl₃ is:

(A) +1(B) +2(C) +3(D) +6

Correct Answer: (C) +3

Electrochemistry

23. In an electrochemical cell, oxidation occurs at the:

(A) Cathode(B) Anode(C) Salt bridge only(D) Electrolyte surface only

Correct Answer: (B) Anode

Chemical Kinetics

24. A catalyst increases the rate of a reaction by:

(A) Increasing the equilibrium constant(B) Providing an alternative pathway with lower activation energy(C) Increasing the enthalpy of products(D) Changing the final products

Correct Answer: (B) Providing an alternative pathway with lower activation energy

Solutions

25. Reverse osmosis is commonly used for:

(A) Increasing hardness of water(B) Desalination of water(C) Increasing boiling point(D) Producing colloids

Correct Answer: (B) Desalination of water

CBSE Class 12 Chemistry • Theory PYQ-Based Practice • 25 MCQs