To determine the chemical formula, we refer to the rules of ionic bonding. Iron (III) has a charge of +3 (denoted as "III"), while oxide has a charge of -2 (denoted as "O"). To achieve electrical neutrality in the compound, we need three iron ions to combine with two oxide ions.

Hence, the chemical formula for iron (III) oxide is Fe2O3, representing two iron ions (Fe3+) bonded with three oxide ions (O2-).