What are #"protons"#, #"neutrons"#, and #"electrons"#?
Well, these are all fundamental particles......
Protons and neutrons are massive particles, whereas electrons are particles of negligible mass. Protons and electrons are charged particles, whose sign is opposite. We assign a negative charge to the electron. It would have been a much better scenario for chemists, had the electron been assigned a positive chatge. The point is the charged nuclear particles have an opposite electric charge to charged extranuclear particles.
Within the nucleus, a short-range attractive force operates between the massive particles: as a chemist, I don't have much of clue about this!