Final answer:
An element is oxidized when its oxidation state increases from the reactants to the products in a chemical reaction, which is answer B.
Step-by-step explanation:
Whether an element has been oxidized in a chemical reaction can be determined by the change in its oxidation state. Specifically, an element is considered oxidized if its oxidation state increases from the reactant to the product side of the reaction. As such, the correct answer to whether an element has been oxidized is that B. Its oxidation state is higher in the product than in the reactant.
For example, in the reaction 4Fe(s) + 3O₂(g) → 2Fe₂O₃(s), iron (Fe) starts with an oxidation state of 0 and ends with an oxidation state of +3. This increase in oxidation state indicates that iron has been oxidized. In contrast, oxygen starts with an oxidation state of 0 and ends with an oxidation state of -2, indicating it has been reduced.