Cerium is a soft, ductile, silvery-white metallic chemical element with the symbol Ce and atomic number 58. Cerium is easily oxidated when exposed to air, we usually pack it under oil to store for a longer time, you can clean it with acetone before using. Cerium is the second element in the Lanthanide series. While it often shows the +3 state characteristic of the series, it also exceptionally has a stable +4 state that does not oxidize water. It is also traditionally considered to be one of the rare earth elements. Cerium has no biological role and is not very toxic.