Question

Why is manganese ($Z=25$) more stable in $+2$ state than $+3$ oxidation state?

Answer 1

Atomic number of $Mn=25$.

Electronic Configurtaion$=\left[Ar\right]3d^{5}4s^2$

for $M{n}^{2+}=\left[Ar\right]3d^5$ & $M{n}^{3+}=\left[Ar\right]3d^4$

The electronic configuration for $M{n}^{2+}$ half field $3d$ orbitals, which is highly stable than that for $M{n}^{3+}$