Oxygen therapy is most useful in-

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.