A peroxide is a compound containing an oxygen–oxygen single bond or the peroxide anion . The O?O group is called the peroxide group or peroxo group. In contrast to oxide ions, the oxygen atoms in the peroxide ion have an oxidation state of ?1. The simplest stable peroxide is hydrogen peroxide. Superoxides, dioxygenyls, ozones and ozonides compound are considered separately. Peroxide compounds can be roughly classified into organic and inorganic.