Question

Name a member of the lanthanoid series which is well known to exhibit $+4$ oxidation state.

Answer 1

$\text{Element that exhibits}+4\text{oxidation state}$

Cerium $Ce\left(\right[Xe\left]4F^{2}5d^{0}6s^2\right)$ is well known to exhibit $+4$ oxidation state.
Formation of $C{e}^{4+}$ is favoured by its noble gas configuration $\left[Xe\right]4f^{0}5d^{0}6s^0$.