Assign oxidation numbers in H2SO4 and identify the oxidation state of sulfur.

• A. H = +1, O = −2; S = +6.
• B. Hydrogen +1, Oxygen -2; Sulfur +4.
• C. Hydrogen +1, Oxygen -1; Sulfur +6.
• D. Hydrogen 0, Oxygen -2; Sulfur +7.

Answer: (A)

When assigning oxidation numbers, follow simple rules: hydrogen is almost always +1 in compounds, oxygen is almost always -2, and the sum of all oxidation numbers in a neutral compound must be zero.

For H2SO4, the molecule is neutral, so the total must sum to zero. Hydrogen contributes +2 from two atoms, oxygen contributes -8 from four atoms, giving a net of -6 so far. Let the oxidation state of sulfur be x. Then x + (+2) + (-8) = 0, which yields x = +6. Therefore, sulfur is in the +6 oxidation state, and oxygen is -2 while hydrogen is +1.

If sulfur were +4, the sum would be off (not zero) when you include the standard H(+1) and O(-2) values. Oxygen being -1 would also contradict the common rule for oxide oxygens in most sulfuric acid contexts, and hydrogen being 0 would imply no contribution from hydrogen in a compound, which isn’t correct here.