Question

What are polar and non polar molecules.

Answer 1

The molecules in which the "centre of gravity" of nucleus does not coincide with the centre of gravity of revolving electrons since they have a permanent dipole moment.
eg. $H_O,N_{2}O$ etc are polar molecules
The molecule in which the centre of gravity of molecule coincide with elections are known as non-polar molecules they don't have permanent dipole moment
e.g. $H_2,N_2$ etc.