PSEB/ NCERT CLASS 12 CHEMISTRY CHAPTER 3 AND 4 MCQS

Class 12 Chemistry MCQ Quiz – Chemical Kinetics & d/f-Block

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Chapter 3 — Chemical Kinetics (Section A – MCQs)

1) The rate constant of a reaction is 0.01 s-1. How much time does it take for 2.4 mol L-1 concentration of reactant to reduce to 0.3 mol L-1?

a) 108.3 s-1 b) 207.9 s-1 c) 248.2 s-1 d) 164.8 s-1

Correct answer: b) 207.9 s-1

2) What time does it take for reactants to reduce to 3/4 of initial concentration if the rate constant is 7.5 × 10-3 s-1?

a) 38.4 s b) 40.2 s c) 39.3 s d) 36.8 s

Correct answer: a) 38.4 s

3) What is the formula to calculate the time taken for the completion (100%) of a zero-order reaction?

a) t_100% = [A]0 / k b) t_100% = [A]0 / 2k c) t_100% = 2[A]0 / k d) t_100% = [A]0 / 3k

Correct answer: a) [A]0 / k

4) The half-life of a given reaction is doubled if the initial concentration of the reactant is doubled. What is the order of the reaction?

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

Correct answer: a) 0

5) For a pseudo first-order reaction, what is the unit of the rate of the reaction?

a) s-1 b) mol L-1 s-1 c) mol-1 L s-1 d) mol-2 L2 s-1

Correct answer: a) s-1

6) Which of the following reactions is an example of a pseudo first-order reaction?

a) H2 + Br2 → 2HBr b) CH3CHO → CH4 + CO c) C12H22O11 + H2O → glucose + fructose d) PCl5 → PCl3 + Cl2

Correct answer: c) Sucrose hydrolysis

7) Which of the following is NOT similar between a first-order and pseudo first-order reaction?

a) The molecularity is one in both the reactions b) Both follow first-order kinetics c) The unit of rate constant is s-1 d) The rate of the reaction depends only on one reactant

Correct answer: a) The molecularity statement

8) In the Maxwell–Boltzmann distribution, what happens to the peak of the curve when temperature increases?

a) Shifts forward and upward b) Shifts forward and downward c) Shifts backward and upward d) Shifts backward and downward

Correct answer: b) Shifts forward and downward

9) Which of the following explains the increase in the reaction rate by a catalyst?

a) Decreases rate of backward reaction b) Provides extra energy to molecules c) Provides an alternative path of lower activation energy d) Increases number of collisions

Correct answer: c) Alternative path with lower E_a

10) What factors determine an effective collision?

a) Translational collision and energy of activation b) Threshold energy and proper orientation c) Proper orientation and steric bulk of the molecule d) Collision frequency, threshold energy and proper orientation

Correct answer: d) All three factors

Chapter 4 — d and f Block Elements (Section A – MCQs)

11) In an experiment to study the trends in ionic radii of lanthanides, which property is being investigated?

a) Magnetic property b) Lanthanide contraction c) Formation of coloured complexes d) Catalytic activity

Correct answer: b) Lanthanide contraction

12) A student compared magnetic properties of Fe2+ and Fe3+ ions. Fe2+ shows 4 unpaired electrons while Fe3+ shows 5 unpaired electrons. Which statement is correct?

a) Fe2+ is more paramagnetic b) Fe3+ is more paramagnetic c) Both are diamagnetic d) Both show equal magnetic moment

Correct answer: b) Fe3+ is more paramagnetic

13) Assertion (A): Transition elements form coloured compounds. Reason (R): This is due to d–d electronic transitions within partially filled d-orbitals.

a) Both A and R are true, and R explains A b) Both A and R are true, but R does not explain A c) A true, R false d) A false, R true

Correct answer: a) R explains A

14) The catalytic activity of transition metals depends on their ability to adopt multiple oxidation states. Which of the following reactions demonstrates this property?

a) 2H2 + O2 → 2H2O (Pt) b) N2 + 3H2 → 2NH3 (Fe) c) 2SO2 + O2 → 2SO3 (V2O5) d) All of the above

Correct answer: d) All of the above

15) Which of the following is a property of lanthanoids?

a) Constant ionic radius across the series b) Gradual decrease in ionic size with increasing atomic number c) No variable oxidation states d) Colourless compounds only

Correct answer: b) Gradual decrease in ionic size

16) Assertion (A): Actinoids show greater tendency towards complex formation than lanthanoids. Reason (R): Actinoids have larger atomic size than lanthanoids.

a) Both A and R true, R explains A b) Both A and R true, but R does not explain A c) A true, R false d) A false, R true

Correct answer: c) A true, R false

17) The element used in nuclear reactors among actinoids is:

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

Correct answer: d) All of these

18) Solutions of KMnO4 are intensely coloured because of:

a) Mn7+ with unpaired d-electrons undergoing d–d transitions b) Charge transfer from oxygen to Mn in MnO4- c) Both a and b d) None of the above

Correct answer: b) Charge-transfer

19) 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

Correct answer: b) High corrosion resistance

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

a) Ti b) Cr c) V d) Mn

Correct answer: a) Ti