Cerium is one of the lanthanides. Electronic configuration of cerium is given below.

${}_{58}\mathrm{Ce}\to \left[\mathrm{Xe}\right] 4{\mathrm{f}}^1 5{\mathrm{d}}^1 6{\mathrm{s}}^2$

As per the electronic configuration of cerium, it has the ability to show $+2$ and $+4$ oxidation states.

${\text{Ce}}^{\text{3+}}\to \left[\text{Xe}\right]{\text{ 4f}}^{\text{1}}{\text{ 5d}}^{\text{0}}{\text{ 6s}}^{\text{0}}$ (common in all Lanthenoids)

${\mathrm{Ce}}^{4+}\to \left[\mathrm{Xe}\right] 4{\mathrm{f}}^0 5{\mathrm{d}}^0 6{\mathrm{s}}^0$