(1) Intermolecular van der Waals' force exists between atoms of noble gases. The magnitude of these forces increases with increasing atomic mass which directly related to boiling point.
(2) As ionisation energy of helium is maximum, thus, electrons are lightly held to the nucleus and therefore has least tendency to form compound.
(3) As valence shells of noble gases are complete, thus they do not show tendency to gain electrons. Therefore, they have zero electron affinity.
(4) As Xenon has lowest ionisation energy, they have maximum number of compounds.