In the first series of transition elements, the oxidation states which lead to exactly half-filled or completely filled \(d\)-orbitals are more stable. For example, \(\mathrm{Mn}(\mathrm{Z}=25)\) has electronic configuration [Ar] \(3 d^5 4 s^2\). It shows oxidation states \(+2\) to \(+7\) but Mn (II) is most stable because of halffilled configuration \([\mathrm{Ar}] 3 d^5\). Similarly \(\mathrm{Sc}^{3+}\) is more stable then \(\mathrm{Sc}^{+}\)and \(\mathrm{Fe}^{3+}\) is more stable than \(\mathrm{Fe}^{2+}\) due to half filled \(d\)-orbitals.