Here's why:

* Molecules are formed when two or more atoms bond together covalently (sharing electrons).

* Ions are atoms or groups of atoms that have gained or lost electrons, resulting in a net electrical charge.

Chlorite ions consist of one chlorine atom and two oxygen atoms, but these atoms are held together by ionic bonds, not covalent bonds. The chlorine atom has gained an electron, giving it a negative charge, while the oxygen atoms share electrons to form a polyatomic ion with a negative charge.

Therefore, chlorite ions are polyatomic ions, not molecules.