[ajax0604]

I am having trouble understanding the order of retention times for methane and propane.
Please refer to the attached jpg for the question and chromatogram.
The solutions say that S is methane and R is propane because methane is smaller and can make its way through the column faster.
I am not satisfied with this explanation because it doesn't explain which molecule has a greater attraction to the stationary phase.
Would propane be more attracted to the stationary phase because it can set up stronger instantaneous dipoles?
Or would it be more attracted to the non-polar mobile phase (I am assuming that this is normal phase HPLC) since it has stronger dispersion forces compared to methane? If that is the case, shouldn't it elute earlier than methane?
Thank you.

[Babcock_Hall]

I hate to say this, but I don't believe that this is a very realistic question; methane and propane are quite volatile and would be better analyzed via gas chromatography.  It would be helpful to know the identity of the mobile phase, but even then it might be difficult to say.