Given that helium's atomic mass is four times greater than that of hydrogen, what is the ratio of helium's diffusion rate to that of hydrogen?

CHEMICAL ENGINEERING MCQs for PPSC, FPSC, NTS, and Pakistan government job tests. Select an option below, then read the explanation.

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Subject
CHEMICAL ENGINEERINGchemical-engineering
Published
12 Mar 2019
Last updated
28 May 2026

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Explanation

According to Graham's law, the diffusion rate of a gas is inversely proportional to the square root of its molar mass. Since helium's atomic weight is 4 times that of hydrogen, the diffusion rate ratio is √(4/1) = 2. Therefore, helium diffuses at 1/√2 times the rate of hydrogen, making the correct choice the square root of two.

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