Why is `Cr^(2+)` acts as reductant and `Mn^(3+)` as oxidant eventhough both have `d^4` configuration ?

Explanation

`Cr^(2+)(d^4)` is less stable than `Cr^(3+)(d^3)` because the latter having a half - filled `t_(2g)` level. Thus `Cr^(2+)` oxidies easily to `Cr^(3+)` and acts as reductant.
`Mn^(3+)(d^4)` is less stable than `Mn^(2+)(d^5)` because the latter has half -filled d-subshell stable electronic configuration. Thus `Mn^(3+)` easily reduced to `Mn^(2+)` and acts as oxidant.