Question

A certain gas takes 3 times as long to effuse out as helium.what will be its molecular mass?

Answer 1

rate of effusion of helium= rHe
rate of effusion of the unknown gas= rˣ
so,
rHe=3 × rₓ
rHe is directly proportional to 1/√M(helium)
rₓ is directly proportional to 1/√M (gas x)

rHe/ rₓ = √M (gas x)/ √M (helium)
3 x rₓ/ rₓ= √M (gas x)/ √M (helium)
√M (gas x) = 3 x √M (helium)
squaring both sides 
M (gas x) = 9 x 4 = 36 g/mol 

Answer 2

The answer is provided in the attachment.

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