(A) : When helium is allowed to expand into vacuum, heating effect is observed.
(R) : The inversion temperature of helium is very low.

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Both (A) and (R) are correct and (R) is the correct explanation of (A)

Both (A) and (R) are correct but (R) is not the correct explanation of (A)

(A) is true but (R) is false

Both (A) and (R) are false

answer is A.

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Detailed Solution

When helium gas is allowed to expand into vacuum, the heating effect is observed.
This is because the inversion temperature of helium is very low.
When a gas is present above the inversion temperature heating is observed.
As inverion temperature is low, the gas is present above the inversion temperature and heating is observed.
Hydrogen and helium exhibit heating effect during Joule - Thomson expansion as work of expansion (during adiabatic expansion).

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