This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Principles of Gas Exchange -  Respiratory Membrane, Subject name: Physiology
pO2 pressure at sea level: 
Select and explain. 
A. 140, B. 150, C. 160, D. 180
C: 160
Answer: C: 160 
Explanation: Ans. (c) 160* At sea level the atmosphere exerts a total pressure of 760mmHg. Since the atmosphere is 21% 02 (by volume), the partial pressure of oxygen (pO,)= 0.21 x 760 = 160 mmHg.* The partial pressure of C02 (pC02) at sea level is 0.23 mmHg.