Final answer:
The oxidizing agent in the reaction 4Fe + 3O₂ → 2Fe₂O₃ is O₂ because it gains electrons and is reduced during the reaction, causing iron to be oxidized.
Step-by-step explanation:
In the reaction 4Fe + 3O₂ → 2Fe₂O₃, to select the oxidizing agent, we need to look at the change in oxidation numbers of the elements. The element iron (Fe) starts as a neutral atom and ends up as Fe³⁺ in Fe₂O₃, meaning it has lost electrons and undergone oxidation. The element oxygen (O₂) gains the electrons that iron has lost because it goes from an oxidization state of 0 in O₂ to a state of -2 in Fe₂O₃. Therefore, O₂ is the oxidizing agent in the reaction because it causes iron to lose electrons, and thus it is being reduced in the process. In this reaction, oxygen is acting as the oxidizing agent, while iron acts as the reducing agent.