Which of the following ions has a charge of -2?

The sulfate ion is indeed a species that carries a charge of -2. It is composed of one sulfur atom centrally located, surrounded by four oxygen atoms. The typical molecular formula for the sulfate ion is SO₄²⁻, indicating the overall negative charge.

In contrast, the other ions listed have different charges. The nitrate ion (NO₃⁻) has a charge of -1, the carbonate ion (CO₃²⁻) has a charge of -2 but is often confused due to its similarity with sulfate, and the phosphate ion (PO₄³⁻) carries a charge of -3. Thus, while carbonate also has a -2 charge, the sulfate ion is a common example often associated with that specific charge and is more prominently recognized in chemical contexts.

Understanding the charges of these common ions is essential in chemistry, particularly in the study of chemical reactions, solution chemistry, and acid-base behavior. Knowing the sulfate ion's -2 charge helps predict its interactions with other ions and compounds in various chemical scenarios.