Given:
No. of moles of
CH4 = 1
No. of moles of unknown gas = 1
Area of orifice through which
CH4 diffusing = 1
mm2 Time = 40 sec
Area of orifice through which unknown gas effusing = 2
mm2 Time = 10 sec
We have to find the molecular mass of unknown gas Let it be M
Molecular mass of
CH4 = 16 g/mol
According to Graham's law of diffusion
r α Area of orifice (i)
where r = Rate of diffusion
Also,
r α
... (ii)
where. M = Molecular mass
Thus, from equation (i) and equation (ii)
=
or
=
.√ ... (iii)
Now,
Rat of diffusion r =
Thus, equation (iii) can be written as
=
.√ or
=
.√ On substituting the values in equation (i). we get
=
.√ =
2 =
√M M = 4
Hence, option 'A' is correct.