Whats the difference between nonpolar and polar in chemistry?

Question

I don't understand how to tell the difference, plz use example

Answer 1

if the forces on the central atom are vectorally equal then dipol moment will be 0 and molecule will be non-polar. Otherwise it is polar

For example:

CH4 ------> C is the central atom and it has 4 hydrogens around it, they apply equal forces on carbon and this is a non-polar molecule but if you replace one of the hydrogens with a Cl atom them balance will be gone(vectorally) so molecule will be polar.

Answer 2

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