The electronic configuration of $\text{Ce}$ is:

$\mathrm{C}\mathrm{e}\mathrm{ }:\left[\mathrm{X}\mathrm{e}\right]\mathrm{ }4{\mathrm{f}}^1\mathrm{ }5{\mathrm{d}}^1\mathrm{ }6{\mathrm{s}}^2$

The most common oxidation states shown by cerium are $\text{+3}$ and $\text{+4}$ .

As energy difference between 4f and 5d-orbitals is very less, so electrons of f-orbitals also take part in bond formation