NEET Biology Breathing And Exchange Of Gases Based Practice Questions & Answers with Viewers Discussion and Detailed Explanation

Answer: (d)

Diffusion is the net flow of a substance from a region of higher concentration to a region of lower concentration. The exchange of gases between the alveoli and blood in the lung is the result of difference in partial pressure of respiratory gases. The partial pressure of oxygen (p$O_2$) of the alveolar air is higher than the p$O_2$ of blood in alveolar capillaries, thus $O_2$ diffuses rapidly from the alveolar air into the blood of alveolar capillaries. The p$CO_2$ of blood reaching the alveolar capillaries is higher than the p$CO_2$ of alveolar air. Therefore, $CO_2$ diffuses into the alveolar air.