one mole of gas occupies 22.4 liters, 5*1/22.4=0.22 moles of carbon dioxide ration of oxygen to carbon dioxide is 1:2 so we divide 0.22 by 2 we get 0.11 moles of oxygen 1 mole occupies 22.4 litres, what if 0.11 moles of oxygen were used what volume would it occupy. so 0.11*22.4/1=2.5L
