Which quantity gives the best indication of the relative strength of the hydrogen bonds between the molecules in liquid hydrogen halides?
a: bond dissociation energies
b: enthalpy changes of formation
c: enthalpy changes of solution
d: enthalpy changes of vaporization
answer is d but how

The hydrogen bonds is an intermolecular force.

This is, it is an atracction among molecules, which trends to keep the molecules  close one to each other quite strongly.

Vaporization is the pass from liquid, where the molecules are pretty close one to each other, to gas, where the molecules are more distant from each other. To reach that separation of the molecules, the strong hydrogen bonds must be overcome, which means a higher energy requirement than in similar compounds without hydrogen bonds.

That is reflected in high values for the enthalpy of vaporization in the compounds with hydrogen bonds (like hydrogen halides).

So, that leads to the option D. of the list of answers. enthalpy heat of vaporization gives the best indication of the relative strenght of hydrogen bonds.