Which noble gas has the highest boiling point? Why?
Boiling point is dependent on the dispersion force of the molecule or atom. Since, the magnitude of the dispersion force depends on the electrons in the atom or molecule which can polarize in response to an instantaneous dipole. This is dependent on the size (or volume) of the electron cloud. The dispersion force would be high when the electron cloud become more which is due to the loose bound with the nucleus and thus polarize easily. Thus, electron cloud will be more when molecules have higher molar mass which results higher dispersion force.
Thus, among all the noble gas, only(c) Rn have higher boiling point. This is because, Rn has higher molar mass which results in higher dispersion force that corresponds to higher boiling point.