Here's the breakdown:

* Calcium (Ca): Calcium is a metal with a +2 charge (Ca²⁺).

* Carbonate Ion (CO₃): This is a polyatomic ion with a -2 charge (CO₃²⁻).

To form a neutral compound, the charges of the ions must balance out. Since the charges are equal and opposite, one calcium ion (Ca²⁺) combines with one carbonate ion (CO₃²⁻) to form CaCO₃.