C.
Explanation:
As a pendulum swings from its highest to its lowest position along an arc, what happens to its kinetic energy and potential energy? The potential energy decreases while the kinetic energy increases.
1 mole of any gas under STP has volume 22.4 L
So 2.50 moles of any gas ( including oxygen)
2.50 mol *(22.4L/1 mol)=56.0 L