The boiling points of the halogens,${\mathrm{F}}_2,{\mathrm{Cl}}_2,{\mathrm{Br}}_2$ and ${\mathrm{I}}_2$ , increase in that order. This is best attributed to differences in strength of :

The elements that make up group 17 of the periodic table, or the halogens, exist as diatomic molecules. These molecules won't display strong London dispersion forces because they are nonpolar.