Question

Assertion (A): Sodium ions are discharged in preference to hydrogen ions at mercury cathode.

Reason (R): The nature of the cathode can affect the order of discharge of ions.

Options

• If both A and R are true, and R is the correct explanation of A.

• If both A and R are true, but R is not the correct explanation of A.

• If A is true, but R is false.

• If both A and R are false.

Answer 1

If both A and R are true, and R is the correct explanation of A.

Explanation:

Normally, hydrogen ions (H⁺) are discharged preferentially over sodium ions (Na⁺) because hydrogen has a lower discharge potential. However, when a mercury (Hg) cathode is used, Na⁺ ions are discharged first because sodium readily combines with mercury to form a stable sodium amalgam (Na/Hg). This phenomenon shows that changing the cathode material can completely alter the preferential order of ion discharge, making R the exact explanation for A.