Correct Answer - A
As the cell is a concentration cell, `E_(cell)^(@)-0`
Now, the cell reaction is
Left electrode:
`H_(2)(P_(1)=640mm)hArr2H^(+)+2e^(-)`
Right electrode:
`:2H^(+)+2e^(-)hArrH_(2)(P_(2)=425mm)`
Net cell reaction:
`H_(2)(P_(1)mm)hArrH_(2)(P_(2)mm)`
Now, from Nernst equation
`=0-(0.059)/(2)log.(425)/(640)=0.005V`