Greatest Change in Sulfur's Oxidation Number

Steps:

• Assign oxidation numbers to sulfur in reactants and products for each reaction.
• Compute the absolute difference (Δ) in sulfur's oxidation number for each option.
• Compare Δ values across options to find the maximum.
• Identify the reaction with the largest Δ as the answer.

Why A is correct:

• Sulfur oxidizes from 0 in S(s) to +4 in SO2(g), yielding Δ = 4, the maximum per oxidation number rules where each O contributes -2.

Why the others are wrong:

• B: Sulfur changes from +4 in SO2 to +6 in SO3, Δ = 2.
• C: Sulfur changes from -2 in H2S to 0 in S(s), Δ = 2.
• D: Sulfur remains +6 in H2SO4 on both sides, Δ = 0.

Final answer: A