At STP, how many liters of $O_2$ can be produced by completely decomposing $2.00$ moles of $KCl{O}_3$?

The correct option is C $67.2$
$2KCl{O}_3\to 2KCl+3O_2$
The decomposition of 2 moles of $KCl{O}_3$ gives 3 moles of oxygen.
At STP, one mole of oxygen ocupies a volume of 22.4 L.
3 moles of oxygen will occupy a volume of $3\times 22.4L=67.2L$.