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Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R: Assertion A: Helium is used to dilute oxygen in diving apparatus. Reason R: Helium has high solubility in O₂. In the light of the above statements, choose the correct answer from the options given below:
Helium is added to diver tanks because of its LOW SOLUBILITY IN BLOOD (prevents the bends). Reason claims "high solubility in O₂", which is completely false and absurd! Assertion A is true, Reason R is false in 10 seconds! (Option 4)
Under high hydrostatic pressure deep underwater, atmospheric gases (especially nitrogen) dissolve in the diver’s blood in large amounts in accordance with Henry’s Law (p = K_H · x). When the diver ascends towards the surface, the ambient pressure decreases, and the dissolved gases are released from solution. Nitrogen forms gas bubbles in the bloodstream, blocking capillaries and causing a severe, painful medical condition known as the bends.
To prevent the formation of nitrogen bubbles and avoid nitrogen narcosis, commercial deep-sea diving breathing mixtures are diluted with helium (typically 11.7% He, 56.2% N₂, and 32.1% O₂). Therefore, Assertion A is completely true.
Helium is utilized specifically because it has an exceptionally high Henry’s law constant (K_H) in water/blood, which corresponds to an extremely LOW SOLUBILITY IN BLOOD. Gases mix in all proportions in the gas phase; claiming that helium is used because it has "high solubility in O₂" is scientifically baseless and factually false.
Assertion A is true, but Reason R is false. This corresponds to Option (4).
Diagnose every choice: Know exactly why the right option works and why distractors fail.
Assertion A is true (helium is indeed used in diving apparatus); Reason R is false.
Reason R is false (helium has low solubility in blood, not high solubility in O₂).
Reason R is false.
Accurate: Assertion A is factually true, while Reason R is scientifically false.
Students who vaguely recall the phrase "solubility of helium" often skim Reason R, see the word "solubility", and automatically assume it is true. The true textbook reason is LOW solubility in BLOOD, not high solubility in oxygen!
"To avoid bends and toxic effects of high concentration of nitrogen in blood, tanks used by scuba divers are filled with air diluted with helium because of its low solubility in blood."
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