What is the oxidation number of the sulfur atom in SO_4^{2-}?

• A. +6
• B. 0
• C. -2
• D. +4

Answer: (A)

Verified step by step guidance

1. Recall that the sulfate ion is \(\mathrm{SO_4^{2-}}\), which consists of one sulfur atom and four oxygen atoms, and the overall charge on the ion is \(-2\).
2. Assign the oxidation number of oxygen as \(-2\) because oxygen almost always has an oxidation state of \(-2\) in compounds (except in peroxides or when bonded to fluorine).
3. Let the oxidation number of sulfur be \(x\). Since there are four oxygen atoms, the total contribution from oxygen is \$4 \times (-2) = -8$.
4. Write the equation for the sum of oxidation numbers equal to the overall charge of the ion: \(x + (-8) = -2\).
5. Solve the equation for \(x\) to find the oxidation number of sulfur: \(x = -2 + 8\).