Question

which problem of atomic structure was solved by the discovery of neutron

Answer 1

The problem was that the time when the neutron was not discovered , many scientists found that the atomic mass of many atoms was found to be double or more than double the mass of total number of protons(as the mass of electron was so small that it was assumed to be negligible), so by the discovery of neutron led to the solution of this problem. FOr eg.- The mass of Carbon-12 atom is 12 u but the no. of protons were 6 so it becomes 6u , which is not correct. 

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Answer 2

Before the discovery of neutron ot was found that the atomic mass of many atoms were double or more than the number of protons. which was solved after the discovery of neutron as there must be some atomic particle which has mass but no charge.