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

Explanation

`Mn^(2+)` ion has electronic configuration `[Ar]3d^(5)`. 3d orbital is half-filled and stable. Due to this, the third ionization enthalpy is very high. The removal of the third electron is difficult.
On the other hand, `Fe^(2+)` has electronic configuration `[Ar]3d^(6)`. Loss of one electron results in stable `[Ar]3d^(5)` electronic configuration. In this 3d orbital, orbital will be half-filled which leads to stability. Hence, removal of the third electron is easy.