text: You need to relax.  Science isn't difficult.  You only think it is because you've always been told it is.  Take a deep breath.\n\nImagine that a pure comound, in this case a liquid, is composed of a bunch of tiny balls.  (This analogy only goes so far so don't count on it forever.)  Anyway, you want to apply sufficient heat on these balls to get them popping around (boiling).  So, of three, namely H2S, H2O and HF which ones pop first?  If you said the lightest ones would tke the least energy, you'd be on your way.  Except that some of these balls stick to each other (beware O as it sticks mightily to hydrogens in other atoms.  This is known as "hydrogen bonding".)  The answer, I think, would be that HF (MW = 20 Da; BP = -84 C) boils before H2S (MW = 34 Da; BP = -60 C) boils before H2O (MW = 18; BP = 100 C).\n\nThe aim of this question is to get you to see that hydrogen bonding complicates boiling point series, especially for water which is only the most important solvent on earth.  Otherwise, the lighter the molecule the lower the boiling point.\n\nThere's no dissociation involved in boiling points other than that dissolved salts raise boiling points and lower freezing ponts.  Molality has to do with number of particles more than molar mass so it's got to be the number of particles physically interfering with the boiling and freezing processes.  You can actually calculate how much effect a salt has on phase changes given the concentration for the salt but that's a different lesson.\n\nGood luck.