Pick out incorrect statements abou noble gases.

Options

A. Ar' is used in metallurgical processes
B. He' is used in cryoscopy to obtain the very low temperatures required for superconductivity and lasers
C. He' is used in weather balloons and airships
D. He' cannot be used in preference to nitrogen `(N_2)` to dilute the oxygen in the gas cylinders used by divers.

Answer

D

Explanation

Helium is used in preference to nitrogen to dilute oxygen in gas cylinders used by divers. This is because nitrogen is quite soluble in blood, so a sudden change in pressure caused degassing and gives bubbles of `N_2` in the blood. This causes the painful (or fatal) condition, called 'bends'. Helium is only slightly soluble, so the risk of bends is reduced.
a) Ar is used to provide inert atmosphere.
b) Helium has the lowest boiling point of any liquid.
c) Though `H_2` has a lower density and is cheaper and more readily available than He, helium is used in weather balloons and airships, because `H_2` is highly inflammable.