Respuesta :
Answer is: iron is oxidized to form rust.
Chemical reaction: Fe + O₂ → Fe₂O₃.
Oxidation half reaction: Fe⁰ → Fe⁺³ + 3e⁻ /×4; 4Fe⁰ → 4Fe⁺³ + 12e⁻.
Reduction half reaction: O₂⁰+ 4e⁻ → 2O⁻²/×3; 3O₂⁰+ 12e⁻ → 6O⁻².
Balanced chemical reaction: 4Fe + 3O₂ → 2Fe₂O₃.
Oxidation is increase of oxidation number, iron is oxidized from oxidation number 0 (Fe) to oxidation number +3 (in rust Fe₂O₃).