Final answer:
The substance that undergoes oxidation in the chemical reaction Fe₂O₃ + 3CO → 2Fe + 3CO₂ is carbon monoxide (CO).
Step-by-step explanation:
The substance that undergoes oxidation in the chemical reaction Fe₂O₃ + 3CO → 2Fe + 3CO₂ is CO (carbon monoxide).
In this reaction, carbon monoxide (CO) is being oxidized to carbon dioxide (CO₂). Oxidation occurs when an element or compound loses electrons. In the case of carbon monoxide, it gains oxygen and its oxidation number increases from +2 to +4.
The iron (III) oxide (Fe₂O₃) is being reduced to iron (Fe) in this reaction. Reduction occurs when an element or compound gains electrons. In the case of iron (III) oxide, it loses oxygen and its oxidation number decreases from +3 to 0.