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

Explanation

Electronic configuration of `Mn^(2+)` is [Ar] `3d^5` which is half filled and hence it is stable. Therefore, third ionisation enthalpy is very high i.e., third electron cannot be easily removed. In case of `Fe^(2+)` , the electronic configuration is `3d^6`. Therefore, `Fe^(2+)` can easily lose one electron to acquire `3d^5` stable electronic configuration.