What are carbohydrates the main source of for all living organisms?

Do you mean "why"?

They are the main source for all living organisms because they provide energy, relatively short term, for any creature that consumes them.

The proton has a positive charge while the neutron has no charge they both make up the nucleus of the atom while the elections have a negative charge and surround the nucleus of the atom. the protons and electrons are used to calculate the atom's mass whereas the neutrons don't affect the mass