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 . In the light of the above statements, choose the correct answer from the options given below.
Answer: (B) Both A and R are true and R is NOT the correct explanation of A. \textbf{Answer:} (B) Both A and R are true and R is NOT the correct explanation of A (official key) \textbf{Solution:} Assertion (A) is correct: helium is mixed with oxygen as a breathing gas for deep-sea divers.
- A.Both A and R are true and R is the correct explanation of A
- B.Both A and R are true and R is NOT the correct explanation of A✓
- C.A is true but R is false
- D.A is false but R is true
Correct Answer
(B) Both A and R are true and R is NOT the correct explanation of A
Solution & Explanation
\textbf{Answer:} (B) Both A and R are true and R is NOT the correct explanation of A (official key) \textbf{Solution:} Assertion (A) is correct: helium is mixed with oxygen as a breathing gas for deep-sea divers. However, note the chemistry carefully. The reason helium is used is precisely that it has \textbf{low} solubility in blood. By Henry's law the amount of a gas dissolved at the high pressures experienced at depth is proportional to its partial pressure. A highly soluble gas like nitrogen dissolves in the blood under pressure and, on ascent, comes out of solution to cause decompression sickness (the \textit{bends}). Helium's very low solubility avoids this, which is why it dilutes the oxygen. The Reason (R) as worded — "Helium has high solubility in " — is therefore chemically incorrect; helium actually has low solubility. The official key marks option (B), so it is retained here, but students should understand that the genuinely correct statement is the \textit{low} solubility of helium (which would make R the correct explanation of A).