The term "carbonate" refers to a polyatomic ion (CO₃²⁻) and not an element or a neutral compound. Therefore, it doesn't have a mass number.

Mass number is specifically used for atoms, which consist of protons and neutrons in their nucleus. It represents the total number of protons and neutrons in an atom.

However, you can calculate the molar mass of the carbonate ion (CO₃²⁻), which is the mass of one mole of the ion.

Here's how to calculate the molar mass of carbonate:

* Carbon (C): 12.01 g/mol

* Oxygen (O): 16.00 g/mol x 3 = 48.00 g/mol

* Total: 12.01 + 48.00 = 60.01 g/mol

Therefore, the molar mass of the carbonate ion (CO₃²⁻) is 60.01 g/mol.