Iodine, atomic number 53, symbol I, is a solid nonmetallic element of the HALOGEN family, a group that includes the elements fluorine, chlorine, and bromine. At room temperature iodine is a lustrous, blue-black, crystalline solid of atomic weight 126.9045. Iodine is the least water-soluble halogen, but it dissolves readily in alcohol, chloroform, carbon tetrachloride, and benzene. Sometimes used as a swimming pool sanitizer, it is noted for a distinctive greenish tint it gives to the water.