Electronic configuration of Mn²⁺ is [Ar]¹⁸3d⁵ and Electronic configuration of Fe²⁺ is [Ar]¹⁸ 3d⁶ . It is known that half-filled and fully-filled orbitals are more stable. Therefore, Mn in (+2) state has a half-filled stable configuration, whereas the Fe in +3 oxidation state has partially filled subshells, which are relatively unstable. This is the reason Mn²⁺ shows resistance to oxidation to Mn³⁺. Also, Fe²⁺ has 3d⁶ configuration and by losing one electron, it attains half-filled stable configuration. Hence, Mn²⁺ compounds more stable than Fe²⁺ towards oxidation to their +3 state.