Cerium (Z = 58) is an important member of the lanthanoids. Which of the following statements about cerium is incorrect?

The +4 oxidation state of cerium is not known in solutions

The correct answer is (3), the +4 oxidation state of cerium is not known in solutions.

The common oxidation states of cerium are +3 and +4. The +3 oxidation state is more stable than the +4 oxidation state, and cerium (IV) acts as an oxidizing agent.

The +4 oxidation state of cerium is known in solid compounds, but it is not known in solutions. This is because the +4 oxidation state is unstable in water, and it will quickly disproportionate to form cerium(III) and cerium(IV) oxide.