Ba2+ (barium ion)

OH- (hydroxide ion)

In barium hydroxide, the barium atom loses two electrons to form a positively charged barium ion (Ba2+). Each hydroxide ion consists of one oxygen atom and one hydrogen atom. The oxygen atom gains two electrons to form an oxide ion (O2-), while the hydrogen atom loses an electron to form a hydrogen ion (H+). The hydroxide ion is formed by the combination of the oxide ion and the hydrogen ion.