Hydrogen against oxygen.

At the same temperature, the speed of sound in hydrogen gas compared with that in oxygen gas (both diatomic) is:

Answer: 4 times larger.

Both gases are diatomic, so they have the same ratio of specific heats γ, and at the same temperature the speed of sound depends only on the molar mass, as one over its square root.

\frac{v_{H_{2}}}{v_{O_{2}}} = \sqrt{\frac{M_{O_{2}}}{M_{H_{2}}}} = \sqrt{\frac{32}{2}} = 4

Sound travels 4 times faster in hydrogen. Forgetting the square root gives 16. The pressure and the density do not matter separately, only their ratio, and at a fixed temperature that ratio is set by the molar mass.

Original practice question · JEE Physics Decoded

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