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

Explanation

The decreasing negative electrode potentials of `M^(2+)//M` in the first transition series (See "Chapter At A Glance" Point 12) shows that in general, the stability of +2 oxidation state decreases from left to right (the exceptions being Mn and Zn). The decrease in the negative electrode potentials is due to increase in the sum `IE_(1)+IE_(2)`. The greater stability of +2 state for Mn is due to half-filled d-subshell `(d^(5))` in `Mn^(2+)` and that of Zn is due to completely filled of subshell `(d^(10))` in `Zn^(2+)`.