Why is `Cr^(2+)` reducing and `Mn^(3+)` oxidising when both have `d^(4)` configuration ?

Explanation

`._(24)Cr^(2+)`, with outer electronic configuration `3d^(4)`, can lose one electron to form `Cr^(3+)` which has the stable `3d^(3)` configuration (half - filled `t_(2g)` level,). On the other hand, `._(25)Mn^(3+)`, with the same outer electronic configuration `3d^(4)`, can gain one electron to form `Mn^(2+)` having stable `3d^(5)`configuration (half - filled d - subshell). So `Cr^(2+)` is reducing while `Mn^(3+)` is oxidising in nature.