In lanthanoids +3 oxidation state is predominant. However occasionally +2 and +4 ions in the solution or in solid compounds arealso obtained. $\text{e.g. } \mathrm{Ce}^{4+}, \mathrm{Tb}^{4+}, \mathrm{Eu}^{2+}, \mathrm{Yb}^{2+}, \text{etc. } +2$ and $+4$ oxidation statesare exhibited due to extra stability of empty, half-filled or fully filled$f-$subshells.