The tanks used by scuba divers are filled with air diluted with helium to ____.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → avoid bends.
Henry’s law: at a constant temperature, the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above it. Helium is much less soluble in blood than nitrogen, so diluting the air with helium helps to avoid bends.
Why the other options are incorrect
Option (1) increase solubility of atmospheric gases. — Incorrect. The aim is the opposite: to reduce the amount of gas dissolving in the blood.
Option (3) increase concentration of nitrogen. — Incorrect. Dissolved nitrogen causes the bends, so helium is added to lower its proportion.
Option (4) avoid anoxia. — Incorrect. Anoxia is caused by the low partial pressure of oxygen at high altitudes, which leaves climbers weak and unable to think properly; it is not the problem of divers.
NCERT (2026-27 edition):
Solubility of a Gas in a Liquid – …
