<P> A polyatomic ion, also known as a molecular ion, is a charged chemical species (ion) composed of two or more atoms covalently bonded or of a metal complex that can be considered to be acting as a single unit . The prefix poly - means "many," in Greek, but even ions of two atoms are commonly referred to as polyatomic . In older literature, a polyatomic ion is also referred to as a radical, and less commonly, as a radical group . In contemporary usage, the term radical refers to free radicals that are (not necessarily charged) species with an unpaired electron . </P> <P> An example of a polyatomic ion is the hydroxide ion; consisting of one oxygen atom and one hydrogen atom, hydroxide has a charge of − 1 . Its chemical formula is O H. An ammonium ion is made up of one nitrogen atom and four hydrogen atoms: it has a charge of + 1, and its chemical formula is N H . </P> <P> Polyatomic ions are often useful in the context of acid - base chemistry or in the formation of salts . A polyatomic ion can often be considered as the conjugate acid / base of a neutral molecule . For example, the conjugate base of sulfuric acid (H SO) is the polyatomic hydrogen sulfate anion (HSO). The removal of another hydrogen ion yields the sulfate anion (SO </P>

What is an example of a polyatomic ion
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