Separate this redox reaction into its component half-reactions. 3o2 4cr

Balanced chemical reaction: 3O₂ + 4Cr → 2Cr₂O₃.

a) Oxidation half-reaction: Cr → Cr⁺³ + 3e⁻ / * 4; 4Cr → 4Cr⁺³ + 12e⁻.

b) Reduction half-reaction: 4e⁻ + O₂ → 2O⁻² / * 3; 12e⁻ + 3O₂ → 6O⁻².

Oxidation is increase of oxidation number (chromium from zero to + 3) and reduction is decrease of oxidation number (oxygen from zero to - 2).