A selenide is a chemical compound containing a selenium anion with oxidation number of -2 (Se^2-), much as sulfur does in a sulfide. The chemistry of the selenides and sulfides is similar. Similar to sulfide, in aqueous solution, the selenide ion, Se^2-, is prevalent only in very basic conditions. In neutral conditions, hydrogen selenide ion, HSe^-, is most common. In acid conditions, hydrogen selenide, H₂Se, is formed.