What are hydroxyl ions?

Hydroxide or hydroxyl ion is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a covalent bond, and carries a negative electric charge.
It is an important but usually minor constituent of water. It functions as a base, a ligand, a nucleophile and a catalyst. The hydroxide ion forms salts, some of which dissociate in aqueous solution, liberating solvated hydroxide ions. Hydroxide ion and hydroxyl group are nucleophiles and can act as a catalyst in organic chemistry.