Final answer:
The polyatomic ion CO3 2- is named carbonate, which must remain intact as a single unit in the formulas of ionic compounds.
Step-by-step explanation:
The polyatomic ion with the formula CO3 2- is named carbonate. When writing the formulas of ionic compounds that contain polyatomic ions such as carbonate, it is important to note that the polyatomic ion acts as a single unit and must remain intact. For instance, calcium carbonate is written as CaCO3, and it is composed of a calcium cation (Ca2+) and a carbonate anion (CO32-). If more than one polyatomic ion is needed to balance the charge, parentheses are used around the polyatomic ion with a subscript outside to indicate the number of ions, as seen in calcium nitrate, which is Ca(NO3)2.