Explanation: Two moles of magnesium reacts with one mole of oxygen gas to form two moles of magnesium oxide. Therefore 2 moles of magnesium = 48 grams. Therefore 2 moles of magnesium oxide = 80 grams. So, 48 grams of magnesium reacts with 32 grams of oxygen to form 80 grams of magnesium oxide.