The balanced reaction from the problem is 2KCIO -> 2KCI + O2 So if 303g of KCI is formed that is approximately 1.702 mol (303 g / MW of KCI (178 g/mol)). For every 2 moles of KCI formed there is 1 mole of O2 formed. Therefore, 0.851 mol of O2 are produced and multiplying by the MW of oxygen (32 g/mol) will yield 27.23 g of oxygen.