Why is `+2` oxidation state of mmanganese quite stable while the same is not true for iron?`[Mn=25,Fe=26]`.

Answer

`Mn^(2+)` has the configuration `[Ar]^(18)3d^(5) 4s^(0)`. It has half-filled configuration and hence is very stable . It is difficult to remove electron from it to converts in into `Mn^(3+)` . On the other hand, `Fe^(2+)` has the configuration `[Ar]3d^(6) 4s^(0)` it can lose electron to from `Fe^(3+)` and give the stable half-filled configuration of `[Ar]3d^(5)`. Hence , `Fe^(3+)` will be more stable than `Fe^(2+)`.