In our universe whatever we see, the smaller constituent are consider as atom. Atom is the smaller unit of any elements or compound.
Nucleus is the centre of an atom which is consists with proton and neutron. Proton is positively charged and neutron is charge neutral. Therefore, nucleus is positively charged.
At first from Rutherford alpha particle scattering experiment we find the structure of atom and the behavior of nucleus.
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Science discussion 