Four successive members of the first series of the transition metals are listed below. For which one of them the standard potential `(E_(M^(2+)//M)^(@))` value has a positive sign?

Options

A. `Cu(Z= 29)`
B. `Fe(Z= 26)`
C. `Co( Z=27)`
D. `Ni(Z= 28)`

Explanation

Copper does not liberate `H_(2)` gas from acids and thus shows positive valueof `E^(@) ( E^(@) ` for `Cu^(2+)//Cu`is `+0.34V)`. For other metals, `E^(@)` value is negative.