Assertion: In the electrolysis of aqueous NaCl, Na is preferentially discharged at mercury cathode forming sodium amalgam.
Reason: It is due to the fact that hydrogen gas a high over voltage at mercury cathode.
A. if both assertion and reason are true and the reason is the correct explanation of the assertion.
B. If both assertion and reason are true but reason is not the correct explanation of the assertion.
C. If assertion is true but reason is false
D. If the assertion and reason both are false.