Question

1g of mg is burnt with 2.5g of oxygen in a closed vessel, at the end of reaction which reactant is left in excess and how much

Answer 1

2 Mg + O2 = 2 MgO

48.64 g of Mg consume 32 g oxygen
1 g Mg will consume 32/48.64 = 0.658 g

Therefore excess oxygen remain = 2.5 - 0.658 = 1.842 g