Final answer:
Hydrogen is 3)oxidized when silver is tarnished by H₂S, leading to the formation of silver sulfide and the release of hydrogen gas as part of a redox reaction.
Step-by-step explanation:
When silver is tarnished by H₂S, hydrogen is oxidized. In the reaction, 2 Ag(s) + H₂S(g) → Ag₂S(s) + H₂(g), silver (Ag) reacts with hydrogen sulfide (H₂S) to form silver sulfide (Ag₂S) and hydrogen gas (H₂).
The sulfur from H₂S is reduced as it forms a bond with silver, thus becoming part of solid Ag₂S, and the hydrogen (H₂) is released as a gas, having been oxidized.
This exemplifies a redox reaction where hydrogen sulfide acts as a reducing agent, and it is its sulfur that is being oxidized to elemental sulfur or to other oxidation states such as SO₃²⁻ or SO₄²⁻ in certain conditions.