Punjab board class 12 Chemistry sample Paper september 2026 -Set 3

CLASS-XII: CHEMISTRY (THEORY) — SET 3

Term-1 / September Examination (2026–27)

Time Allowed: 3 Hours | Maximum Marks: 70

General Instructions

1. There are 21 questions in this question paper with internal choice.

2. SECTION A consists of 1 question (Q1) with 18 sub-parts carrying 1 mark each. Sub-parts (i) to (xvi) are Multiple Choice Questions, and (xvii) to (xviii) are Assertion-Reasoning questions.

3. SECTION B consists of 12 Very Short Answer questions (Q2 to Q13) carrying 2 marks each. Internal choice is provided in three questions.

4. SECTION C consists of 6 Short Answer & Case Study questions (Q14 to Q19) carrying 3 marks each. Internal choice is provided in two questions. Q19 is a Case Study question.

5. SECTION D consists of 2 Long Answer questions (Q20 and Q21) carrying 5 marks each. Internal choice is provided in both questions.

6. Use of log tables and unprogrammable calculators is allowed.

Blue Print & Weightage Summary

Chapter Name	Section A (1M)	Section B (2M)	Section C (3M)	Section D (5M)	Total Marks
1. Solutions	3 (3M)	2 (4M)	1 (3M)	—	10 Marks
2. Electrochemistry	3 (3M)	2 (4M)	—	1 (5M)	12 Marks
3. Chemical Kinetics	3 (3M)	2 (4M)	1 (3M)	—	10 Marks
4. d- and f-Block Elements	3 (3M)	2 (4M)	1 (3M)	1 (5M)	15 Marks
5. Coordination Compounds	3 (3M)	2 (4M)	2 (6M)	—	13 Marks
6. Biomolecules	3 (3M)	2 (4M)	1 (3M)	—	10 Marks
Total Marks	18 Marks	24 Marks	18 Marks	10 Marks	70 Marks

SECTION A (18 Marks)

Q1. Select and write the most appropriate option for the following sub-parts:

(i) In the laboratory, a student observes that water boils at a higher temperature after adding a non-volatile solute. This observation is explained by:

(a) Raoult's law (b) Henry's law (c) Charles's law (d) Graham's law

(ii) Which of the following is a colligative property?

(a) Surface tension (b) Viscosity (c) Osmotic pressure (d) Refractive index

(iii) If 1 mole of NaCl is dissolved in water, the observed colligative property is nearly double than expected. The reason is:

(a) Association of solute (b) Dissociation of solute (c) Non-ideal solution (d) Henry's law deviation

(iv) In electrolysis, Faraday's first law states that:

(a) Mass of substance deposited is proportional to current and time (b) Mass depends on voltage only (c) Mass depends on temperature only (d) None of these

(v) A student wants to electroplate a copper spoon with silver. Which setup is correct?

(a) Spoon as anode, silver as cathode (b) Spoon as cathode, silver as anode (c) Both spoon and silver as cathode (d) Spoon as anode, silver nitrate not required

(vi) A student removes the salt bridge from a Daniell cell while the cell is operating. What happens immediately?

(a) Cell voltage increases (b) Electron flow continues normally (c) Current soon stops because charge builds up (d) Zinc dissolves faster

(vii) For a reaction A + 2B → C, the rate law is given by Rate = k[A][B]². What is the overall order of the reaction?

(a) 1 (b) 2 (c) 3 (d) 0

(viii) The decomposition of gaseous ammonia on a hot platinum surface at high pressure is a:

(a) Zero-order reaction (b) First-order reaction (c) Second-order reaction (d) Third-order reaction

(ix) For the reaction 2N₂O₅(g) → 4NO₂(g) + O₂(g), if the rate of disappearance of N₂O₅ is 2.0 × 10⁻⁴ mol L⁻¹s⁻¹, what is the rate of formation of NO₂?

(a) 1.0 × 10⁻⁴ mol L⁻¹s⁻¹ (b) 2.0 × 10⁻⁴ mol L⁻¹s⁻¹ (c) 4.0 × 10⁻⁴ mol L⁻¹s⁻¹ (d) 8.0 × 10⁻⁴ mol L⁻¹s⁻¹

(x) Chromium is used in stainless steel manufacturing. Which property makes it suitable?

(a) Formation of volatile oxides (b) High corrosion resistance due to Cr₂O₃ layer (c) Colourful compounds (d) High density

(xi) Which of the following elements is used in nuclear reactors among actinoids?

(a) Thorium (b) Uranium (c) Plutonium (d) All of these

(xii) Which transition element is commonly used in artificial satellites for corrosion resistance?

(a) Ti (b) Cu (c) V (d) Mn

(xiii) The coordination number of the central metal atom in [PtCl₄]²⁻ is:

(a) 2 (b) 4 (c) 6 (d) 8

(xiv) Which type of ligand is ethylenediamine (en)?

(a) Monodentate (b) Bidentate (c) Tridentate (d) Polydentate

(xv) Which of the following complexes is tetrahedral?

(a) [Ni(CN)₄]²⁻ (b) [NiCl₄]²⁻ (c) [Co(NH₃)₆]³⁺ (d) [Fe(CN)₆]³⁻

(xvi) Vitamin 'C' is the chemical compound called:

(a) Riboflavin (b) Ascorbic acid (c) Rabinose (d) Thiamine

Directions for sub-parts (xvii) and (xviii):

In each of the following questions, a statement of Assertion (A) is followed by a statement of Reason (R). Choose the correct option:

(a) Both (A) and (R) are true, and (R) is the correct explanation of (A). (b) Both (A) and (R) are true, but (R) is not the correct explanation of (A). (c) (A) is true, but (R) is false. (d) (A) is false, but (R) is true.

(xvii)

Assertion (A): In a galvanic cell, oxidation takes place at the anode.

Reason (R): The anode releases electrons during the oxidation process.

(xviii)

Assertion (A): Sucrose is a non-reducing sugar.

Reason (R): In sucrose, the reducing groups of glucose and fructose are involved in glycosidic bond formation.

SECTION B (24 Marks)

Q2. If a solution shows an elevation in boiling point of 0.52 K, calculate the molar mass of the solute. The ebullioscopic constant (K_b) for water is 0.52 K kg mol⁻¹ and the mass of solute used is 2 g in 100 g of water. (2 Marks)

Q3. Explain the term "molality" and describe how it differs from molarity. Why is molality preferred over molarity for measuring concentrations at varying temperatures? (2 Marks)

Q4. The standard emf of a galvanic cell is 0.0591 V at 298 K with n = 1. Calculate the equilibrium constant (K_c) for the cell reaction. (2 Marks)

Q5. A conductivity cell containing 0.01 M KCl solution has a resistance of 50 Ω. If the cell constant is 0.4 cm⁻¹, calculate: (2 Marks)

(a) Conductivity (κ)

(b) Molar conductivity (Λ_m)

OR

A car battery discharges during normal use. (2 Marks)

(a) Name the electrolyte used in a lead-acid battery.

(b) What happens to the concentration and density of H₂SO₄ during discharge?

Q6. Distinguish between the Order and Molecularity of a chemical reaction with two points of difference. (2 Marks)

Q7. Calculate the half-life of a first-order reaction having rate constant k = 4.93 × 10⁻⁴ s⁻¹. (2 Marks)

Q8. Zirconium (Zr) and Hafnium (Hf) exhibit almost identical chemical properties and ionic radii. Justify this observation. (2 Marks)

Q9. Why do transition metals exhibit variable oxidation states in their compounds? (2 Marks)

OR

Why do zinc (Zn), cadmium (Cd), and mercury (Hg) have comparatively low melting and boiling points? (2 Marks)

Q10. Differentiate between double salts and coordination compounds with a suitable example of each. (2 Marks)

Q11. Explain the chelate effect. Why are chelating complexes generally more stable than non-chelated complexes? (2 Marks)

Q12. What is mutarotation? Explain with reference to α- and β-anomers of D-glucose. (2 Marks)

Q13. State two important structural or chemical differences between DNA and RNA. (2 Marks)

OR

Differentiate between reducing sugars and non-reducing sugars with one example of each. (2 Marks)

SECTION C (18 Marks)

Q14. The boiling point of benzene is 353.23 K. When 1.80 g of a non-volatile, non-electrolyte solute was dissolved in 90 g of benzene, the boiling point increased to 354.11 K. Calculate the molar mass of the solute (K_b for benzene = 2.53 K kg mol⁻¹). (3 Marks)

Q15. The rate constant for a first-order reaction is 60 s⁻¹. How much time will it take to reduce the initial concentration of the reactant to 1/10^th of its initial value? (3 Marks)

OR

A first-order reaction takes 23.1 min for 50% completion. Calculate the time required for 75% completion of this reaction. (3 Marks)

Q16. Give scientific reasons for the following observations: (3 Marks)

(a) Transition metals and their compounds show paramagnetism.

(b) Transition metals easily form interstitial alloys.

(c) The +2 oxidation state of lead (Pb) is more stable than that of tin (Sn).

Q17. (3 Marks)

(a) What are ambidentate ligands? Give two examples.

(b) Write the formula of two coordination complexes showing linkage isomerism.

OR

Explain the difference between high-spin (outer orbital) and low-spin (inner orbital) octahedral complexes with one example of each. (3 Marks)

Q18. Differentiate between ionisation isomerism and hydrate (solvate) isomerism. Give one example formula for each type. (3 Marks)

Q19. CASE STUDY QUESTION

Read the passage below and answer the questions that follow:

A radioactive isotope used in medical oncology undergoes first-order nuclear decay. Unlike zero-order processes where the reaction rate is independent of substrate concentration, the rate of a first-order process is directly proportional to the reactant concentration at any given instant. Furthermore, the half-life period (t_1/2) of a first-order reaction is completely independent of the initial concentration ([R]₀) of the substance. Medicines and radio-pharmaceuticals frequently display shelf-life stability governed by Arrhenius temperature kinetics.

(a) On which kinetic parameters does the half-life of a first-order reaction depend? (1 Mark)

(b) If the half-life of a medical radioisotope sample is 4 hours, what fraction of the radioactive substance remains undecayed after 8 hours? (1 Mark)

(c) Why are certain medicinal drugs recommended to be stored at low temperatures in refrigerators? (1 Mark)

SECTION D (10 Marks)

Q20.

(a) For the cell:

Ni(s) | Ni²⁺(0.01 M) || Cu²⁺(0.01 M) | Cu(s)

Calculate the cell EMF (E_cell) at 298 K and formulate the Nernst equation for the cell reaction.

[Given: E°(Ni²⁺/Ni) = −0.22 V, E°(Cu²⁺/Cu) = +0.34 V] (3 Marks)

(b) The resistance of a 0.5 M solution of an electrolyte placed between two platinum electrodes 1.5 cm apart and having cross-sectional area of 2.0 cm² was found to be 30 Ω. Calculate the molar conductivity (Λ_m) of the solution. (2 Marks)

OR

(a) Calculate the maximum electrical work (W_max = −ΔG°) that can be obtained from the standard Daniell cell:

Zn(s) | Zn²⁺(aq) || Cu²⁺(aq) | Cu(s)

[Given: E°(Zn²⁺/Zn) = −0.76 V, E°(Cu²⁺/Cu) = +0.34 V, 1 F = 96,500 C mol⁻¹] (3 Marks)

(b) Answer the following: (2 Marks)

(i) Write the cathode and anode reactions occurring during the electrolysis of aqueous CuSO₄ using copper electrodes.

(ii) State one major advantage and one limitation of fuel cells compared to conventional batteries.

Q21.

(a) Explain the following: (3 Marks)

(i) Catalytic behaviour of transition metals based on variable oxidation states and surface adsorption.

(ii) Why actinoids exhibit a wider range of oxidation states compared to lanthanoids.

(iii) Why Cr²⁺ acts as a strong reducing agent whereas Mn³⁺ acts as a strong oxidising agent.

(b) (2 Marks)

(i) What is the general electronic configuration of d-block transition elements?

(ii) Explain why Cu⁺ is unstable in aqueous solution and undergoes disproportionation.

OR

(a) Account for the following: (3 Marks)

(i) Enthalpy of atomization of transition metals is quite high.

(ii) Transition metal ions generally form coloured complexes in aqueous solution.

(iii) Basic strength of lanthanoid hydroxides Ln(OH)₃ decreases progressively from La(OH)₃ to Lu(OH)₃.

(b) Write balanced chemical structures/equations for the preparation of potassium dichromate (K₂Cr₂O₇) from chromite ore or explain the interconversion of chromate and dichromate ions with change in pH. (2 Marks)