# IChO problem involving the condensation point of NF3, NHF2, NH2F

This is a problem from the 2016 International Chemistry Olympiad (IChO):

Which of $\ce{NF3}$, $\ce{NHF2}$, and $\ce{NH2F}$ condenses at the lowest temperature?

The answer book says that it is $\ce{NF3}$. But I don't understand why. In $\ce{NF3}$, $\ce{N}$ should have the greatest positive charge of the three molecules; therefore, it should have the highest b.p., no?

Maybe the answer lies in somewhere in the geometry of ions. Can't figure out what. Any hint?

What's special about $\ce{NF3}$? It has no hydrogens. As a result, it cannot form hydrogen bond, therefore its boiling point (or condense point) is far lower than the others'.