Final answer:
The average paO2 of blood on the arterial side of a pulmonary capillary bed at rest is approximately 100 mm Hg.
Step-by-step explanation:
The average paO2 of blood on the arterial side of a pulmonary capillary bed at rest is approximately 100 mm Hg. This is because oxygen is diffusing down its pressure gradient from the alveoli, where the partial pressure of oxygen is about 104 mm Hg, to the blood in the capillaries, where the partial pressure of oxygen is about 40 mm Hg. This significant pressure gradient facilitates the rapid diffusion of oxygen across the respiratory membrane.