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
What is the paial pressure for oxygen in the expired air? 
Select and explain. 
A. 116 mm Hg, B. 158 mm Hg, C. 100 mm Hg, D. 0.3 mm Hg
A: 116 mm Hg
Answer: A: 116 mm Hg 
Explanation: Paial pressure of O2 in expired air (PE O2) - 116 mm Hg Gaseous concentration & its paial pressure in alveoli: 1. Oxygen: Concentration & paial pressure controlled by, Rate of absorption of O2 into blood Rate of entry of new O2 into lungs by ventilatory process. Values: Paial pressure of O2 in inspired air (Pi O2) 158 mm Hg Paial pressure of O2 in alveolar air (PA O2) 100 mm Hg Calculated by "Alveolar gas equation". Paial pressure of O2 in expired air (PE O2) 116 mm Hg