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
In hyperventilation: 
Select and explain. 
A. P50 and Hb affinity for O2 increases, B. P50 and Hb affinity for O2 decreases, C. P50 increases and O2 affinity decreases, D. P50 decreases and O2 affinity increases
D: P50 decreases and O2 affinity increases
Answer: D: P50 decreases and O2 affinity increases 
Explanation: Hyperventilation washes out CO2 from body, leadng to alkalosis.So, Oxygen hemoglobin dissociation  curve will  shift  to  left  (high  affinity), decreasing P50 of hemoglobin.
Reference: Ganong’s Review of Medical Physiology 24th edition pg 611