the balanced equation for the reaction between Mg and O₂ is as follows 2Mg + O₂ --> 2MgO stoichiometry between Mg and O₂ is 2:1 number of Mg reacted - 4.00 mol if 2 mol of Mg reacts with 1 mol of O₂ then 4.00 mol of Mg requires - 1/2 x 4.00 = 2.00 mol of O₂ then the mass of O₂ required - 2.00 mol x 32.0 g/mol = 64.0 g 64.0 g of O₂ is required for the reaction