$I_2$ molecules are held in the solid lattice by $...................$

Among the following,the weakest one is:

The dipole-dipole interaction energy between stationary polar molecules and rotating polar molecules,respectively,is proportional to: [$r$ is the distance between the polar molecules]

Which of the following has the minimum melting point?

Total number of molecules which have cation-anion pair out of $I_{2(s)}$,dry ice $(CO_{2(s)})$,$PCl_{5(s)}$,$N_2O_{5(s)}$,$PBr_{5(g)}$ is

Give reasons: Graphite is used as a lubricant.