Although +3 oxidation states is the characteristic oxidation state of lanthanoidsbut cerium shows +4 oxidation state also. Why?
Ce – [Xe] 4f1 5d1 6s2. Usually lanthanoids lose the 5d and 6s electrons and show +3 oxidation state, but Cerium loses the one 4f electron also so as to attain Xenon’s noble gas configuration which will make Ce4+ very stable.