Krypton has a higher melting point than argon because of its?

Inert gases have London Dispersion forces operating between them. These dispersion forces also increase with increasing atomic mass of the inert gas. I mean Krypton will have greater amount of dispersion forces operating between its atoms as compared with Argon due to its higher mass. these dispersion forces are interactions occurring between instantaneous dipoles that generate in the atom as a result of rotating electrons around the nucleus. Higher the nuclear charge more is the value of such instantaneous dipoles and therefore higher the interactive forces and hence higher the melting point. Answer will be choice -II