Identify the species oxidized. 2 al3 + (aq) + 2 fe (s) → 2 al (s) + 3 fe2 + (aq)

To know the answer, compare the oxidation number of the element in the reactant and the product side. The oxidation number of Al was originally + 3, then became 0 after the reaction. On the other hand, Fe was originally 0, then became + 2 after the reaction. When the element is oxidized, it oxidation number increases. Thus, the element oxidized is Fe.