What is the oxidation number of sulfur in H₂SO₄?

• The oxidation number of hydrogen is +1 (Rule #3).
  There are two hydrogen atoms.
• The oxidation number of oxygen is -2 (Rule #6).
  There are four oxygen atoms.
• The overall charge of the compound is zero, so the sum of the oxidation numbers of all the atoms in the formula is zero (Rule #8).

Let the oxidation number of sulfur be represented as S.

2(+1) + 4(-2) + S = 0

-6 + S = 0

S = +6