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

Options

A. `Mn^(2+)` is more stable with high 3rd ionisation energy
B. `Mn^(2+)` is bigger in size
C. `Mn^(2+)` has completely filled d-orbitals
D. `Mn^(2+)` does not exist