For which of the molecules will dipole-dipole interactions be important?

Answer: is seen below

Explanation:

Firstly, Dipole-Dipole interactions result when two dipolar molecules (intermolecular) interact with each other through space. When this interaction occurs, the partially negative portion of one of the polar molecules is attracted to the partially positive portion of the other polar molecule. To determine whether a bond is polar or not, you look at the electronegativity difference between the atoms. If the electronegativity difference is between 0.4 and 1.7, then it is considered to be a polar bond.

Example of intermolecular interaction is hydrogen bound, example could be between a partially positively charged hydrogen in one molecule and a partially negatively charged oxygen, fluorine or nitrogen in a nearby molecule.