Assertion`(A):` Whne acidified `ZnSO_(4)` solution is electrolyzed between `Zn` electrodes, it is `Zn` that is deposited at the cathode and `H_(2)(g)` is not evolved.
Reason `(R):` The electrode potential of `Zn` is more negative than hydrogen as the overpotential for hydrogen evolution in `Zn` is quite large.

Options

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.

Answer

A

Explanation

Two reactions are possible at cathode: `H^(+)(aq) + e^(-) rarr (1)/(2)H_(2)(g) E^(@)= 0`
`Zn^(2+)(aq)+ 2e^(- ) rarr Zn(s) E^(@) lt 0`
It is true that the electrode potential of zinc is more negative than hydrogen. So hydrogen gas should evolve at the cathode. But the over voltage for the hydrogen evolution on zinc is quite large so zinc will deposit at the cathode. Hence reason is the correct explanation for assertion.