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Question:

A mixture of 2 moles of helium gas (atomic mass = 4 amu) and 1 mole of argon gas (atomic mass = 40 amu) is kept at 300 K in a container. The ratio of the rms speeds (vrms(helium)/vrms(argon)) is:

0.32

3.16

0.45

2.24

Solution:

Vrms=√(3RT/M)
Thus we get required ratio as=√(MAr/MHe)=√(40/4)=√10=3.16