`Cr^(2+)` is reducing as its configuration changes from `d^(4)` to `3d^(4)`, the latter having a halg-filled t^(3)`_(2g)` energy level of `3d` orbitals in octahedral crystal field soliting . On the other hand , the change from `Mn^(3+)`result in the half-filled `(d^(5))` configuration which has extra stability. Therefore(C) is correct.
