Question

Assertion (A): In the electrolysis of aqueous NaCl, Na is preferentially discharged at the mercury cathode forming sodium amalgam.
Reason (R) : It is due to the fact that hydrogen has a high over voltage at mercury cathode.

• A. Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
• B. Both Assertion and Reason are true but Reason is not a correct explanation of Assertion.
• C. Assertion is true but Reason is false.
• D. Assertion is false but Reason is true.

Answer 1

The correct option is A Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Assertion (A): In the electrolysis of aqueous NaCl, Na is preferentially discharged at the mercury cathode forming sodium amalgam.

$2N{a}^{+}+2e^{-}\to 2NaNa+Hg\to NaHg\left(\text{sodium amalgam}\right)$

Reason (R) : Hydrogen has a high over voltage at mercury cathode. Hydrogen should be discharged in preference to sodium. However, this does not happen because of the high over-potential of hydrogen over mercury.

Hence, both Assertion and Reason are true but Reason is the correct explanation of Assertion.