What is the formula of the sulphate ion?

What is the formula of the sulphate ion?

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

Answer: (A)

The key idea is recognizing the formula and charge of a polyatomic ion. The sulphate ion consists of one sulfur atom surrounded by four oxygen atoms and carries a total charge of 2−. Check the overall charge by oxidation states: sulfur is +6, each oxygen is −2, so four oxygens contribute −8. +6 plus (−8) gives −2, which matches the ion’s 2− charge. That makes the correct formula SO4^2−. The other options describe different species: for example, three oxygens would be sulfite (SO3^2−); a four-oxygen species with zero or unclear charge isn’t the sulphate ion; and a two-oxygen species like SO2 would be a different compound altogether.

The key idea is recognizing the formula and charge of a polyatomic ion. The sulphate ion consists of one sulfur atom surrounded by four oxygen atoms and carries a total charge of 2−. Check the overall charge by oxidation states: sulfur is +6, each oxygen is −2, so four oxygens contribute −8. +6 plus (−8) gives −2, which matches the ion’s 2− charge. That makes the correct formula SO4^2−.

The other options describe different species: for example, three oxygens would be sulfite (SO3^2−); a four-oxygen species with zero or unclear charge isn’t the sulphate ion; and a two-oxygen species like SO2 would be a different compound altogether.