Which ion has the formula SO4 2-?

• A. SO4 2-
• B. SO3 2-
• C. SO4 0-
• D. SO2-

Answer: (A)

Think about polyatomic ions formed from sulfur and oxygen. The sulfate ion is built from one sulfur atom surrounded by four oxygen atoms and carries an overall charge of 2−. That exact combination—four oxygens with a total −2 charge—defines SO4^2−. In resonance, the negative charge is spread over the oxygens, typically shown as two S=O bonds and two S–O− bonds, but the overall charge remains −2. The sulfur is in the +6 oxidation state in this ion, which helps explain why the four-oxygen, −2 charge arrangement is stable and distinct.

The other possibilities don’t match this exact composition: three oxygens with a −2 charge would be sulfite, a different ion; a neutral four-oxygen set isn’t the same charged species; and other formulas with fewer oxygens don’t describe sulfate.