Answer:
Protons and neutrons
Explanation:
Nucleus is the central dense part of the nucleus and consists of most of the mass of an atom.
An atom has three subatomic particles:
Electrons are negatively charged subatomic particles, protons are positively charged and neutrons are neutral.
Electrons are present in the energy shells outside to the nucleus and revolve around it.
Protons and neutrons are present in nucleus.
Number of protons and neutrons present in the nucleus together called mass number or atomic mass.
Therefore,
Atomic mass = No. of protons + No. of neutrons
Number of protons present in the nucleus is same as the number of electrons present outside nucleus.
Therefore,
No. of protons = No. of electrons = Atomic number
