The decreasing negative electrode potentials of `M^(2+)//M` in the first transtion series ( see Table on page) shows that t 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 d- subshell `(d^(10))` in `Zn^(2+)`.
