Electrochemistry and Electrolysis – NDA Chemistry PYQs

Solve NDA Chemistry previous-year questions on Electrochemistry with detailed solutions and explanations.

Chapter-wise PYQs • Concept-based explanations • Exam insights

NDA 2022-II

Q. 1. Which one of the following solutions is not capable of conducting electricity?

(a) Copper sulphate

(b) Sodium chloride

(d) Sodium hydroxide

Answer: (c) Sugar

Explanation: Sugar (C₁₂H₂₂O₁₁) is a covalent molecule that dissolves in water but does not ionise – it produces no free ions and therefore cannot conduct electricity. CuSO₄, NaCl and NaOH all dissociate into ions in solution and conduct electricity. Concept Tested: Non-electrolyte – sugar solution does not conduct electricity

NDA 2021-I

Q. 2. In electrolytic refining of copper, the electrolyte is a solution of

(a) acidified copper chloride.

(b) acidified copper sulphate.

(d) sodium sulphate.

Answer: (b) acidified copper sulphate.

Explanation: In electrolytic refining of copper, the electrolyte is acidified copper sulphate (CuSO₄ + H₂SO₄). The impure copper acts as the anode (dissolves), pure copper deposits at the cathode, and the copper concentration in the electrolyte is maintained.
Concept Tested: Electrolytic refining of copper – acidified CuSO₄ electrolyte

NDA 2017-II

Q. 3. Which compound, when dissolved in water, conducts electricity and forms a basic solution?

(a) HCl

(b) CH₃COOH

(d) NaOH

Answer: (d) NaOH

Explanation: NaOH (sodium hydroxide) dissociates fully in water: NaOH → Na⁺ + OH⁻. It conducts electricity (free ions) and forms a basic (alkaline) solution. HCl conducts but is acidic. Acetic acid conducts weakly and is acidic. Methanol does not conduct and is neutral.
Concept Tested: Electrolyte giving basic solution – NaOH

NDA 2015-I

Q. 4. Why is Graphite used in electrolytic cells ?

(a) Graphite is soft and can be easily moulded into electrodes

(b) Graphite is made of layers of carbon atoms which can slide

(d) Graphite is a good conductor of electricity

Answer: (c) Graphite is inert to most of the chemicals and remains intact in electrolytic cells

Explanation: The most important reason graphite is used as an electrode in electrolytic cells is its chemical inertness – it does not react with electrolytes or products of electrolysis. While it is also a good conductor (d), the primary reason for electrode use is inertness. If it conducted but was reactive, it would dissolve in the electrolyte.
Concept Tested: Graphite electrodes in electrolysis – chemical inertness