Climbers at high altitudes may become weak and unable to think clearly, a condition known as anoxia. What is the cause of this condition?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → The partial pressure of oxygen is low, so the concentration of oxygen in the blood and tissues is low
The amount of a gas that dissolves in a liquid is proportional to the partial pressure of the gas above it (Henry’s law). At high altitudes the partial pressure of oxygen is less than at ground level, so less oxygen dissolves in the blood. This low blood oxygen causes anoxia.
Why the other options are incorrect
Option (1) Bubbles of nitrogen form in the blood as the pressure falls and block the capillaries — Incorrect. This is bends, which affects scuba divers coming up towards the surface, not climbers.
Option (3) The partial pressure of oxygen is high, so too much oxygen dissolves in the blood and tissues — Incorrect. The partial pressure of oxygen at high altitudes is lower, not higher, than at ground level.
Option (4) The partial pressure of nitrogen is low, so the concentration of nitrogen in the blood and tissues is low — Incorrect. The weakness and confusion come from a shortage of oxygen; less dissolved nitrogen does not cause anoxia.
NCERT (2026-27 edition):
1.3.2 Solubility of a Gas in a Liquid – “• At high altitudes the partial pressure of oxygen is less than that at the ground level. This leads to low concentrations of oxygen in the blood and tissues of people living at high altitudes or climbers. Low blood oxygen causes climbers to become weak and unable to think clearly, symptoms of a condition known as anoxia.”