Why are `Mn^(2+)` compounds more stable than `Fe^(2+)` towards oxidation to their +3 state?

Explanation

The electronic configuration of `Mn^(2+) " is " 1s^(2) 2s^(2) 2p^(6) 3s^(2) 3p^(6) 3d^(5)`. To oxidize to `Mn^(3+)`, the one electron has to be removed from state `d^(5)` orbital which is half filled and requires high ionization energy. In `Fe^(2+)` ion, the third electron is taken from `3d^(6)` configuration that results in more stable `3d^(5)` configuration.