Melting point of p− Chlorobenzene is higher than o-Chlorobenzene because of its closed packed structure which have high intramolecular forces of attraction. That's why high amount of temperature is required to break down the bonds while boiling point of o-chlorobenzene is high because of high dipole interaction present at ortho-position. There is great dipole-dipole forces of attraction between carbon and chlorine atom which results into high boiling point as compared to p-chlorobenzene which have zero dipole moment.