What is the correct formula for the carbonate ion?

The formula for the carbonate ion is CO₃²⁻. This correct choice indicates that there are three oxygen atoms bonded to a single carbon atom, and the overall charge of the ion is negative two. The carbonate ion is a common polyatomic ion found in various chemical compounds, such as calcium carbonate (CaCO₃), which is commonly found in limestone and marble.

In terms of the structural components, the carbonate ion comprises one carbon atom centrally located and bonded to three oxygen atoms in a trigonal planar configuration, which can be represented by resonance structures. This stability arises from the delocalization of electrons among the oxygen atoms.

The other options presented are not correct because:

• The first choice, CO(2-), implies a molecule that does not conform to the arrangement or charge expected for a carbonate ion.

• The third choice, CO₂(-), suggests the presence of two oxygen atoms bonded to carbon with a single negative charge, which does not correspond to the typical carbonate specification.

• The fourth choice, CO₂(2-), also misrepresents the correct number of oxygen atoms, indicating two, while the carbonate ion includes three.

Thus, the correct formula accurately reflects both the composition and the charge of the carbonate ion.