No of moles of Fe = Mass / Relative molar mass of Fe. So no of moles = 89.4/ 55.845 = 1.60. The. Chemical reaction is represented as follows. 4 Fe + 3 O2 which gives 2Fe2 O3 . This means that 4 atoms of Iron reacts with 3 atoms of Oxygen to produce Iron oxide. Hence 1.60*4 moles of Fe will need to react 1.6 * 3 moles of Oxygen to produce 2 moles of Iron oxide. Hence 4.8 moles of Oxygen will be required.