Answer :
According to the law of conservation of mass, the mass of reactants must be equal to the mass of products.
The balanced chemical reaction is,
As we know that the molar mass of magnesium is 24 g/mole, the molar mass of is 32 g/mole and the molar mass of magnesium oxide is 40 g/mole.
From the given balanced reaction, we conclude that
As, 1 mole of magnesium react mole of oxygen to give 1 mole of magnesium oxide.
So, the mass of Mg is 24 g, the mass of and the mass of MgO is 40 g.
That means 24 g of Mg react with 16 g to give 40 g of MgO.