`E^@` (standard electrode potential) values generally become less negative as we move across a transition series. But `E^@`values of `Ni^2//Ni` and `Zn^(2+)//Zn` are exceptions. Justify.

Explanation

The values of `E^@` for `Ni^(2+)//Ni ` and `Zn^(2+)//Zn`are more negative than expected. The high negative value `E^@Ni^(2+)//Ni ` is due to the high enthalpy of hydration of `Ni^(2+)` + ions. This stabilises `Ni^(2+)`ions. The high negative value of `E^@Zn^(2+)//Zn` is due to the stable completely filled `3d^10` electronic configuration of `Zn^(2+)` ions.