The oxidation state of sulfur in sulfuric acid, H₂SO₄, is +6. Oxygen is assigned an oxidation state of −2 and hydrogen is assigned +1, so the neutral molecule gives the equation 2(+1) + S + 4(−2) = 0, requiring sulfur to be +6.
Oxidation state is a bookkeeping system for tracking how electrons are distributed in a compound; it does not necessarily mean that sulfur exists as a simple free ion with a full +6 charge. In sulfuric acid, sulfur is covalently bonded to oxygen, but the oxidation-state calculation formally assigns the bonding electrons according to standard rules.
Sulfuric acid is a strong diprotic acid. It can donate two protons in separate stages, producing hydrogen sulfate and then sulfate ions. It is also a powerful dehydrating agent and, especially when concentrated, can cause severe chemical burns and remove water from organic materials.
The distractor values describe other sulfur states or situations: elemental sulfur has oxidation state 0, while +2 and +4 occur in some sulfur compounds. Sulfur’s common oxidation states range broadly, from −2 in hydrogen sulfide to +6 in sulfuric acid and sulfate compounds.