# What are polyatomic ions?

Polyatomic ions are molecular species that happen to have a charge, an excess or deficiency of electrons; e.g. $N {O}_{3}^{-} , C l {O}_{4}^{-} , S {O}_{4}^{2 -}$.
Take the neutral oxygen molecule, $O = O$, add 2 electrons, and we have the peroxide ion, ""^(-)O-O^-. Of course, this species is associated with ${K}^{+}$/$N {a}^{+}$ counterions; how many?