Compare the stability of +2 oxidation state for the elements of the first transition series.

Explanation

The electrode potentials of `M^(2+) | M` decreases in the first transition series and therefore, in general, the stability of +2 oxidation state decreases from left to right (except for Mn and Zn). The decrease in the negative electrode potential, `E^@(M^(2+)| M) ` is due to the increase in the sum of `IE_1+IE_2`. However, the greater stability of +2 oxidation state for Mn is due to half filled d subshell `(3d^5)` in `Mn^(2+)` and that of Zn is due to completely filled d subshell `(3d^10)` in `Zn^(2+)`.