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Consider a mixture of gas molecule of types A, B and C having masses mA < mB < mC. The ratio of their root mean square speeds at normal temperature and pressure is:

1. vA = vB = vC = 0
2. 1/vA > 1/vB > 1/vC
3. vA = vB ≠ vC
4. 1/vA < 1/vB < 1/vC

Correct answer: 1/vA < 1/vB < 1/vC

Solution

Root-mean-square speed is proportional to 1/sqrt(m). Since mA<mB<mC, vA>vB>vC, which means 1/vA<1/vB<1/vC.

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