Why `Fe^3+` is more stable than `Fe^2+` ?

Explanation

The electronic configuration of `Fe, Fe^(2+) and Fe^(3+)` are shown below :
`Fe (Z = 26) = [ ar] 3d^(6) 4s^(2), Fe^(2+) = [Ar] 3d^(6) , Fe^(3+) = [Ar] 3d^(5)`
Here, the electronic configuration of `Fe^(3+)` is more stable (3d-orbitals are all half-filled)
Hence, `Fe^(3+)` is more stable than `Fe^(2+)`