The lanthanoid series consists of the elements with atomic numbers from 57 to 71. The +4 oxidation state is relatively rare among the lanthanoids, but it is most commonly exhibited by Cerium (Ce). Cerium has an oxidation state of +4 in certain compounds, whereas other lanthanoids like Europium and Samarium predominantly show +3 oxidation states.
Thus, the correct answer is:
\[
\text{(3) Cerium}
\]