compare Van der Waals Force

The substance is all the same i.e. Br2

The Van de Waal's force is the intermolecular attraction.

In solid state, Br2 molecules are closely packed.
The attraction between Br2 molecules are the highest.

In gas state, Br2 molecules are separated far apart,
so the attraction is very weak.

The attraction in liquid state is the intermediate.

This is a nice reference:
http://cost.georgiasouthern.edu/chemistry/general/molecule/forces.htm