1.0 g of Mg is burnt with 0.56 g O2  in a closed vessel.  Which reactant is left in excess and how much?

24 g Magnesium requires 16 g of oxygen  0.56 g oxygen requires 0.84 g magnesium As 1g of Mg is taken, weight of magnesium left unreacted = 1 – 0.84 = 0.16g