What is the charge on the sulfate ion?

The sulfate ion, represented as ( \text{SO}_4^{2-} ), has a charge of -2. This is derived from the combined effects of the oxidation states of the sulfur and oxygen atoms within the ion. Sulfur generally has an oxidation state of +6 in sulfate, while each oxygen has an oxidation state of -2. Therefore, the total charge can be calculated as follows:

• Sulfur contributes +6,
• Four oxygen atoms contribute a total of ( 4 \times (-2) = -8 ).

Adding these together shows that the overall charge on the sulfate ion is:

[ +6 + (-8) = -2. ]

This results in the sulfate ion having a net charge of -2. Consequently, the notation ( \text{SO}_4^{2-} ) explicitly indicates this charge, confirming that the correct indication of the sulfate ion's charge is -2, often written in the form of '2-' in various chemical contexts.