Which particle is massive and positively charged in atomic nuclei?

• A. Neutron
• B. Electron
• C. Positron
• D. Proton

Answer: (D)

Inside atomic nuclei, the main constituents are protons and neutrons. Protons carry a positive electric charge, while neutrons have no charge. Electrons and positrons are not part of the nucleus under normal conditions, and they are much lighter than the nucleons. So the particle that is both massive and positively charged within the nucleus is the proton. Neutrons are massive too but neutral, electrons are light and outside the nucleus, and positrons are light antiparticles not typically found in the nucleus.