Before starting your analysis, keep in mind that a higher boiling point implies the presence of stronger intermolecular forces.
Magnesium chloride is an ionic compound, which implies that it is formed by the very strong electrostatic attractions that exist between positively and negatively charged ions.
In this case, the magnesium cations,
Since fluorine is more electronegative than nitrogen, the three
This molecule will exhibit dipole-dipole interactions, which are considerably weaker than ionic bonds. Furthermore, the strength of the dipole moment will be reduced because of the presence of the lone pair of electrons on the nitrogen atom.
SIDE NOTE All the molecules exhibit weak London dispersion forces, but their importance is shadowed by the stronger dipole-dipole interactions and hydrogen bonds present.