Since the chemical formula is Al2O3, it means in a single molecule there are 2 atoms Al and 3 atoms O. O means oxygen and Al means alluminium, so there are 2 atoms alluminium and 3 atoms oxygen.
21.4 g Al * (1 mol / 26.98 g ) * (2 mol Fe / 2 mol Al) = 0.793 mol Fe 91.3 g Fe2O3 * (1 mol / 159.69 g) * (2 mol Fe / 1 mol Fe2O3) = 1.14 mol Fe 0.793 mol Fe * (55.85 g / 1 mol) = 44.3 g Fe produced.
