`E_(M^(2+//M))^(@) ` values are not regular for first row of transition metals (3d-series ) give the reason

Explanation

There is decreasing negative electrode potentials of `M^(2+)` /M in the first transition series due to increase in the sum `IE_(1) + IE_(2)`. It shows that in general, the stability of + 2 oxidation state decreases from left to right (exceptions are Mn and Zn) in which 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 d-subshell `(d^(10)) i n Zn^(2+)`