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

Options

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

Answer

A

Explanation

For hydrogen electrode
`H^(+)(aq)+e^(-)to(1)/(2)H_(2)(g)`
`E=E^(@)-(0.0591)/(1)"log"((p_(H_(2)))^(1//2))/([H^(+)])`
`=-0.0591"log"((p_(H_(2)))^(1//2))/([H^(+)])" "(becauseE^(@)=0)`
E will be -ve when `((p_(H_(2)))^(1//2))/([H^(+)])` is +ve,
i.e., `(p_(H_(2)))^(1//2)gt[H^(+)]` which is so in case of (b).