Which of the following ions carries a formal charge of -2?

To determine which ion carries a formal charge of -2, it's important to consider the common charges associated with each of the given ions.

The bicarbonate ion typically has a formula of HCO₃⁻, indicating it carries a charge of -1 due to the presence of one additional hydrogen atom, making it neutral overall with one less electron than protons.

The carbonate ion is represented as CO₃²⁻. This indicates a formal charge of -2, stemming from the configuration that includes two extra electrons beyond the number of protons. Carbonate is commonly involved in reactions in the carbonate buffer system and in various mineral formations.

The sulfate ion is denoted as SO₄²⁻, which also carries a formal charge of -2. Similar to carbonate, sulfate contains four oxygen atoms bonded to a sulfur atom and results in a net charge of -2.

The phosphate ion, with the formula PO₄³⁻, has a formal charge of -3. This means it has three additional electrons compared to the number of protons, leading to a stronger negative charge than -2.

Out of all these ions, both carbonate and sulfate have a formal charge of -2, but since only one answer can be chosen