Final answer:
The oxidation number of sulfur in H2SO4 is +6, which is necessary to balance the -2 charge from each of the four oxygen atoms and the +1 charge from each of the two hydrogen atoms.
Step-by-step explanation:
The oxidation number of the sulfur atom in H2SO4 can be calculated using the known oxidation numbers for hydrogen (H) and oxygen (O). Hydrogen typically has an oxidation number of +1, and oxygen has an oxidation number of -2. In the compound H2SO4 there are two hydrogen atoms and four oxygen atoms.
Thus, the oxidation numbers for all hydrogens is 2 x (+1) = +2 and for all oxygens is 4 x (-2) = -8. To balance the charges, the remaining oxidation number must be taken by the sulfur (S) atom for the molecule to have a net zero charge. Therefore, sulfur must have an oxidation number of +6 to balance the negative charge contributed by the oxygen atoms.
Based on this, the correct answer to the student's question is: option D) +6