Oxidation State Change of Sulfur

Steps:

• Assign oxidation numbers to sulfur in reactants and products for each reaction.
• Calculate the absolute change in oxidation number for sulfur in each case.
• Compare the magnitudes of these changes across options.
• Select the reaction with the largest change.

Why A is correct:

• Sulfur oxidizes from 0 in S(s) to +4 in SO2(g), a change of 4 units, per oxidation number rules where free elements are 0 and O is -2.

Why the others are wrong:

• B: Sulfur changes from +4 in SO2 to +6 in SO3, a smaller change of 2.
• C: Sulfur changes from -2 in H2S to 0 in S(s), a change of 2.
• D: No reaction occurs; H2SO4 remains +6 in both sides, change of 0.

Final answer: A