Which particles contribute to the mass of an atom and are located in the nucleus?

• A. Electrons
• B. Protons
• C. Neutrons
• D. Protons and neutrons

Answer: (D)

Mass comes from the particles in the nucleus. The nucleus houses protons and neutrons, together called nucleons, and their combined mass makes up most of the atom's mass. Electrons are far lighter and reside outside the nucleus in the electron cloud, contributing very little to the overall mass. So, the particles that contribute to the mass and are located in the nucleus are protons and neutrons. The total mass is essentially the sum of protons and neutrons (the mass number), while the nucleus’s charge comes from the protons.