The one I would expect to have the largest dispersion forces would be the largest and heaviest molecule. This is evidenced by the fact that that molecule is a liquid at room temperature while all the others are gases.
C3H8 = This is propane and a gas at room temperature
F2 = Also a gas at room temperature
BeCl2 = This is a solid and forms an extended lattice in the form of Be-Cl-Be bridges therefore dispersion forces are not important
Therefore the answer to this is C12H26 which is a wax and a liquid at room temperature.
Answer:
C12H26
