What is the chemical formula for the carbonate ion?

The correct answer is the carbonate ion, which has the chemical formula CO3²⁻. This ion consists of one carbon atom bonded to three oxygen atoms, and it carries a net charge of -2. The structure of the carbonate ion features a central carbon atom that is symmetrically surrounded by three oxygen atoms, typically arranged in a trigonal planar configuration. The negative two charge indicates that there are two more electrons associated with the ion than there are protons in the carbon and oxygen atoms.

In the context of the other options, HCO3⁻ represents the bicarbonate ion, which is related but has only one hydrogen and carries a -1 charge. O2⁻ is the peroxide ion, which does not relate to carbon or the carbonate structure. CO2, carbon dioxide, is a neutral molecule composed of one carbon atom and two oxygen atoms; however, it does not carry any ionic charge and does not represent the carbonate ion. These distinctions clarify why CO3²⁻ is the correct representation of the carbonate ion.