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.