[Shahab Mirza]

I'm not convinced at all. In fact, I believe the "answer" 4 is plain wrong.

4 is only the ratio of the mean molecules' speed. To compute a diffusion coefficient, it also needs a mean free path or a mean collision frequency, which depends on the molecule size.

http://en.wikipedia.org/wiki/Diffusion_coefficient#Gases
"sigma is the average collision diameter"

You maybe right sir, but i think in this question we are dealing with Graham's Law , my school friend solved it like this but i think he is wrong see this .
According to Graham's law 

( rate CH4 / rate SO2 ) ^2 = MM SO2 / MM CH4

= 64 / 16 = 4

so rate CH4 / rate SO2 = square root √4 = 2

CH4 diffuses 2 x as fast as SO2


his answer is 2 :/ answer should be 4

[Borek]

Comparative rates of diffusion of He and SO2 will be

( rate CH4 / rate SO2 ) ^2 = MM SO2 / MM CH4

So which one it is: He/SO₂ or CH₄/SO₂?

[Shahab Mirza]

Comparative rates of diffusion of He and SO2 will be

( rate CH4 / rate SO2 ) ^2 = MM SO2 / MM CH4

So which one it is: He/SO₂ or CH₄/SO₂?

yeah sorry , i asked wrong thing Sir, I wanted to ask that is the method for solving both equations same or not , but due to overtime and tiredness i thought that both question are same , sorry :/