This is a stoichiometry problem, where we have an initial amount of reactant and we need to find out how much of the product will we end up with, in order to do that we need to:
1. Set up the properly balanced equation, which the question already provided us
2 KClO3 -> 2 KCl + 3 O2
2. Check the molar ratio between the two compounds, which is 2:3, 2 moles of KClO3 will produce 3 moles of O2, but we have 3 moles of KClO3
2 KClO3 = 3 O2
3 KClO3 = x O2
x = 4.5 moles of O2 will be produced from 3 moles of KClO3
3 KClO3
2 KClO3/ 3 O2
4.5 O2
