The reduction potential of hydrogen half cell will be negative if :

Options

A. `p(H_(2)) = 1` atm and `[H^(+)] = 1.0` M
B. `p(H_(2)) = 2` atm and `[H^(+)] = 1.0` M
C. `p(H_(2)) = 2 ` atm and `[H^(+)] = 2.0` M
D. `p = (H_(2)) = 1 ` atm and `[H^(+)] = 2.0` M

Answer

B

Explanation

For hydrogen electrode .
`H^(+) (aq) + e^(-) to (1)/(2) H_(2) (g)`
`E = E^(@) - (0.0591)/(1) "log" ((pH_(2))^(1//2))/([H^(+)])`
`=-0.0591 log ((pH_(2))^(1//2))/([H^(+)]) (because E^(@) = 0)`
E will be `-ve` when `((pH_(2))^(1//2))/([H^(+)]) ` is +ve.
i.e., `(pH_(2))^(1//2) gt [H^(+)]` which is no case of (b) .