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Why are deep-sea divers given a breathing mixture of helium and oxygen instead of ordinary air?
AHelium increases the partial pressure of oxygen
BHelium is non-toxic, unlike nitrogen
CHelium has lower solubility than nitrogen in blood, reducing the risk of decompression sickness (bends) on ascent
DHelium binds to haemoglobin more readily than nitrogen
Answer & Solution
Correct answer: C. Helium has lower solubility than nitrogen in blood, reducing the risk of decompression sickness (bends) on ascent
At depth, the high pressure dissolves a large amount of breathing gas in blood. Nitrogen has appreciable solubility, so on rapid ascent it comes out of solution as bubbles in the bloodstream, causing decompression sickness ('bends'). Helium has a much lower solubility (higher $K_H$) so it dissolves less under pressure and releases less rapidly on ascent.
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