Question

Why are $M{n}^{2+}$ compounds more stable than $Fe2+$ towards oxidation to their +3 state?

Answer 1

$M{n}^{2+}=1s^2,2s^2{p}^6,3s^2{p}^6{d}^5$ (half-filled d-orbital)
$F{e}^{2+}=1s^2,2s^2{p}^6,3s^2{p}^6{d}^6$

$M{n}^{2+}$ compounds are more stable due to half-filled d-orbitals. $F{e}^{2+}$ compounds are comparatively less stable as they have six electrons in their 3d-orbital. So, they tend to lose one electrons (form $F{e}^{3+}$) and get stable $3d^5$ configuration.