Final answer:
Cerium is an exception among lanthanoids and can exhibit an oxidation state of +4 in addition to its characteristic +3 oxidation state. This is due to its electron configuration and the ability to lose both its 4s and 3d electrons. The ability to exhibit multiple oxidation states is a characteristic of transition metals like cerium.
Step-by-step explanation:
Cerium (Ce) is an element that belongs to the lanthanoid series of the periodic table. Most lanthanoids have a characteristic oxidation state of +3. However, cerium is an exception and can also exhibit an oxidation state of +4. This is due to its electron configuration and the fact that it can lose both its 4s and 3d electrons.
In the ground state, cerium has the electronic configuration [Xe] 4f^1 5d^1 6s^2. When it forms a +3 ion, it loses the two 6s electrons and one 4f electron, resulting in [Xe] 4f^1. However, it can also lose one additional 4f electron and form a +4 ion, which has the electronic configuration [Xe].
This ability to exhibit multiple oxidation states is a characteristic of transition metals and their compounds. Transition metals have partially filled d orbitals, which makes it easier for them to gain or lose electrons and adopt different oxidation states. Cerium, being a transition metal, can therefore exhibit both +3 and +4 oxidation states.