Question

Why does $Ce$ show $+4$ oxidation state ?

Answer 1

The electronic configuration of $Ce$ is $\left[Xe\right]4f^{1}5d^{1}6s^2$

Lanthanides are very less electronegative. Their electronegative value is nearly equal to s-block elements. So they can lose electrons to form a cation. When Cerium loses 4 $e^{-}$,and it will acquire fully field electronic configuration of Xenon (2,8,18,18,8). As fully filed or half filed electronic configuration possesses extra stability.