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Question:

A mixture of 2 moles of helium gas (atomic mass=4u), and 1 mole of argon gas (atomic mass=40u) is kept at 300K in a container. The ratio of their rms speeds [Vrms(helium)/Vrms(argon)], is close to: 0.45, 2.24, 0.32, 3.16

0.45

0.32

3.16

2.24

Solution:

As we know that Vrms = √(3RT/M)
Vrms(He)/Vrms(Ar) = √(MAr/MHe) = √(40/4) = 3.16