Final answer:
The polyatomic ion in Na2O2 is known as peroxide. Peroxide (O2 2-) is a distinct ion from oxide, containing two oxygen atoms with a shared -2 charge.
Step-by-step explanation:
The name of the polyatomic ion in the compound Na2O2 is peroxide. This compound contains two sodium ions and one peroxide ion. In general, polyatomic ions are charged groups of atoms that are bonded together covalently and behave as a single unit within an ionic compound. The polyatomic ion peroxide (O2 2-) consists of two oxygen atoms sharing a -2 charge. This ion is distinct from the regular oxide ion (O2-), which consists of just one oxygen atom and has a -2 charge. When naming ionic compounds containing polyatomic ions, we refer to these ions by their standard names, such as sulfate or nitrate, without indicating the ionic charge in the formula.