Explain in brief the experimental proof which led to the discovery of –
Discovery of Neutrons: As atom contains protons and electrons. The atomic mass of the electron is negligible.
∴ An atom of helium which contains 2 protons should have a mass = (2 × 1) + 0 = 2 a.m.u. But the atomic mass of a helium atom was found to be approximately 4.0 a.m.u. It was, therefore, proved that, in the nucleus of an atom, there is another particle called a neutron which has no electrical charge but is almost of an equal mass as the protons.