Ionic compounds are chemical compounds made of charged ions held together by forces called ionic bonding. Ionic bonds are formed by transfers of valance electrons, which create charged atoms (ions) which are attracted to each other because they have opposite charges. This is not be confused with covalent bonding, in which atoms form an attraction by sharing electrons.

contains a positively charged ion and negatively charged ion which form an ionic bond. contains two positively charged ions and a negatively charged ion which form an ionic bond. , , and are all examples of molecules that contain covalent bonds. None of them contains any charged ions. The answer is therefore "two,"referring to the and molecules.