From the list that follows, choose ALL of the polyatomic ions: Na+ O2- Al3+ OH- PO43- Mg2+ SO42- CN- Li+ Br-?

A polyatomic ion is an ion (cation or anion) which contains 2 or more atoms.

There are 4 polyatomic ions in the list. They are :
1. OH⁻ ion, each contains 2 atoms (1 O atom and 1 H atom)
2. PO₄³⁻ ion, each contains 5 atoms (1 P atom and 4 O atoms)
3. SO₄²⁻ ion, each contains 5 atoms (1 S atom and 4 O atoms)
4. CN⁻ ion, each contains 2 atoms (1 C atom and 1 N atom)

Actually it means more than two atoms. The prefix "poly" means many. Ions containing two atoms eg OH-, CN- etc would normally be referred to as diatomic so the only polyatomic ions in the list are phosphate and sulfate.

polyatomic ion is an ion that contains more than one atom.

PO43- SO42-