Answer
$23.0\text{ L}$
Work Step by Step
$120*0.5=62.5\text{ grams $H_2O_2$}$
$62.5\text{ grams $H_2O_2$}*\frac{1\text{ mol $H_2O_2$}}{34.0147\text{ grams $H_2O_2$}}*\frac{1 \text{ mol $O_2$}}{2\text{ mol $H_2O_2$}}=0.919\text{ mol $O_2$}$
$746\text{ torr}*\frac{1\text{ atm}}{760\text{ torr}}=0.982\text{ atm}$
$PV=nRT$
$0.982*V=0.919*0.08206*300$
$V=23.0\text{ L}$
