In the lungs, the respiratory membrane separates tiny sacs of air (pressure 1.00x105Pa) from the blood in the capillaries. These sacs are called alveoli. The average radius of the alveoli is 0.012 cm, and the air inside contains 20% oxygen. Assuming that the air behaves as an ideal gas at 300K, find the number of oxygen molecules in one of these sacs. Boltzmann constant =1.38 x10-23 J K