The attraction between molecules of methane in the liquid state is primarily due to

Attraction between molecules of methane in liquid state is primarily due to "London dispersion force".

Explanation:

Methane is a non-polar and aprotic molecule. Hence there is no dipole moment in methane as well as no chance of hydrogen bonding formation by methane.

We know that all molecules contain electrons. Therefore transient dipole arises in every molecule due to revolution of electrons around nucleus in a non-circular orbit. Hence an weak intermolecular attraction force is always present in every molecule as a result of this which is termed as "London dispersion force".

So, attraction between molecules of methane in liquid state is primarily due to "London dispersion force".