Explanation: this is a stoichiometry problem.
First, we convert grams of Kcl into moles by dividing by its molar mass:
(15.0 g KCl) x (1 moles/74.55g) = 0.201 moles KCl
Then, we convert moles of KCl to moles of O2 using the molar ratio from the balanced equation:
0.201 moles KCl x (3 moles O2/2 moles KCl) = 0.302 moles O2
Finally, we convert moles of O2 to grams of O2 by multiplying by its molar mass:
0.302 moles O2 x (32 g / 1mole) = 9.66 g O2