Question: which subatomic particles are the most massive?
Answer: Protons have a mass that is 1,836 times that of the electron, at 1.6726×10-27 kg, while neutrons are the most massive of the three, at 1.6929×10-27 kg (1,839 times the mass of the electron). The total number of protons and neutrons in an atoms' nucleus (called "nucleons") is called the mass number.