This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
CO2 diffuse more easily than O2 because: Less dense 
Select and explain. 
A. Less dense, B. More soluble in plasma, C. Less molecular weight of CO2, D. Less pCO2 in the alveoli
B: More soluble in plasma
Answer: B: More soluble in plasma 
Explanation: B i.e. More soluble in plasma - Carbon dioxide (CO2) is 20 times more soluble in water (= plasma) than oxygen (02), this is the reason why CO2 diffuses about 20 times more rapidly than does 02 across the alveolar-capillary barrier (although CO2 has a higher but not very different molecular weight than 02) . Rate of diffusion a solubility/ VMW - Because the transfer of carbon monoxide (CO) across blood gas barrier of lung is limited solely by diffusion, and therefore CO is the gas of choice for measuring the diffusion propeies of lunge.