Answer: C. 11.2 L
Step-by-step explanation:
According to Avogadro's number there are ~6.022 * 10^23 atoms/molecules per mol.
6.022/2 ≅ 3.01, so that means there is half of a mole of oxygen gas. To convert between moles and liters at standard temperature and pressure (STP), multiply the number of mol by 22.4 (the number of liters a single mole of any gas would occupy at STP).
0.5 x 22.4 = 11.2
The units of our final answer would be in liters, so...
3.01 * 10^23 molecules of oxygen gas occupy 11.2 L at STP.