Assume two chemical reactions are linked together in a means that the O2 produced in the first reaction goes on to react completely with Mg to form MgO in the second reaction.
Reaction one: 2 KClO3 ? 3 O2 + 2 KCl
Reaction two: 2 Mg + O2 ? 2 MgO
Suppose you start with 4 moles of KClO3, define how many moles of MgO could eventually form?