Why is `Cr^(2+)` reducing and `Mn^(3+)` oxidizing even though both have the same `d^(4)` electronic configuration.

Explanation

`Cr^(2+)` is reducing as its configuration changes from `d^(4)" to "d^(3)` , the latter having a half-filled `t_(2g)` level. On the other hand, the change from `Mn^(2+)" to "Mn^(3+)` results in the half-filled `(d^(5))` configuration which has extra stability.