Question

What are the types of intermolecular forces acting in the liquid state of krypton? What are the ones acting in the liquid state of nitrogen fluoride?

Answer 1

`Kr`: London dispersion forces.
`NF_3`: London dispersion forces and dipole-dipole forces.

Explanation:

(Assuming nitrogen fluoride refers to `NF_3`.)

In the liquid state of krypton (which would have to be at an extremely low temperature), the only intermolecular forces present would be London dispersion forces.

This is because krypton, being monatomic, is nonpolar.
The only intermolecular forces in nonpolar molecules are London dispersion forces.

`NF_3`, on the other hand, is a different case. This is the Lewis dot structure of `NF_3`:

There is one lone pair around the central nitrogen atom, along with three bonds. So, the VSEPR shape of `NF_3` will be trigonal pyramidal, which means that it's a polar molecule.

The lone pair will push the three bonded pairs, creating a slightly positive end and a slightly negative end.

The polarity of `NF_3` causes there to not only be London dispersion forces (which are present in every molecule), but also dipole-dipole forces.
There are no hydrogen bonds, because `NF_3` doesn't have any `H-F`, `H-O`, or `H-N` bonds.