This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Applied Aspects and Respiratory Adjustments, Subject name: Physiology
Oxygen therapy is most useful in- 
Select and explain. 
A. Anemic hypoxia, B. Hypoxic hypoxia, C. Stagnant hypoxia, D. Histotoxic hypoxia
B: Hypoxic hypoxia
Answer: B: Hypoxic hypoxia 
Explanation: Ans. is 'b' i.e., Hypoxic hypoxia o Administration of oxygen-rich gas mixture is useful when the blood PO2 is low, i.e., in hypoxic hypoxia.o For the same reason, it is of little use in those type of hypoxia in which there is no reduction in arterial PO2, i.e., stagnant (hypoperfusion), anemic and histotoxic hypoxia.o Oxygen treatment is also useless in hypoxic hypoxia if it is due to ventilation-perfusion mismatch, i.e., the deoxygenated blood bypasses the well ventilated alveoli, e.g., in cyanotic congenital heart diseases.