Which particle is a fundamental constituent that combines to form protons and neutrons?

• A. Quark
• B. Electron
• C. Lepton
• D. Boson

Answer: (A)

Quarks are the fundamental constituents that combine to form protons and neutrons. Protons are made of two up quarks and one down quark, while neutrons are made of two down quarks and one up quark. These quarks are held together by gluons, the carriers of the strong force. Electrons are not inside the nucleus; they are leptons, a separate family of fundamental particles that orbit the nucleus and do not bind quarks. Leptons include electrons and neutrinos. Bosons are force-carrier particles, such as photons and gluons, that mediate forces rather than serving as the building blocks of matter.