Here's why:

* Iron (III) indicates that the iron ion has a +3 charge (Fe³⁺).

* Oxide refers to the oxygen ion, which has a -2 charge (O²⁻).

To balance the charges, you need two iron ions (2 x +3 = +6) and three oxygen ions (3 x -2 = -6). This gives you the final formula: Fe₂O₃.