Europium

Europium, a silvery-white metal, is the 63rd element on the periodic table. It's the most reactive, least dense, and softest lanthanide, easily cut with a knife. Isolated in 1901 and named after Europe, europium typically has a +3 oxidation state, but +2 is also common, making those compounds slightly reducing. While it has no major biological role and is less toxic than other heavy metals, europium's phosphorescent properties are widely used. It's one of the rarest rare-earth elements found on Earth.