what is the general relationship between the polarity of the molecules of different substances and the boiling

Question

and can explain why ...

Answer 1

The boiling point depends on the intermolecular forces.
The stronger the intremolecular forces, the more energy you need to break them and thus the higher the boiling point will be.

Polar molecules attract each other through dipole-dipole forces. The higher the polarity, the more strong these forces will be (because you will have stronger dipoles)
Non-polar molecules attract each other through dispersion forces which are much weaker than the dipole-dipole forces.

Therefore polar molecules will have higher boiling points and as polarity increases the boiling point also increases.

Answer 2

In general a polar molecule (like a molten salt or even water) will have a higher boiling point than a non polar one (like ether or octane).

The reason is due to the electrical attraction of the poles of the molecules for one another which tends to bind them together in the liquid.