Molecular weight of x=36g/mol
(According to graham's law of effusion or diffusion, the rate of effusion of a gas is inversely proportional to the square root of the mass of its particles.
RateB
RateA
=
(
molarmassA
molarmassB
)
Let Rate of unknown gas = x; Rate of Helium = 3x; mass of unknown gas = y
mass of He = 4.
x
3x
=
(
4
y
(
4
y
)
=3
squaring on both sides
(
4
y
)
=9
∴y=4×9=36u)
