Leptons as fundamental particles not subject to strong force

Steps:

• Recall that leptons are elementary particles that do not participate in the strong nuclear force.
• Identify the electron as a charged lepton in the Standard Model.
• Eliminate composite particles like protons and neutrons, which are made of quarks.
• Confirm quarks are elementary but belong to the hadron family, not leptons.

Why C is correct:

• The electron is classified as a lepton in the Standard Model of particle physics, one of the six types including neutrinos.

Why the others are wrong:

• A. Proton: Composite baryon made of three quarks, subject to strong force.
• B. Neutron: Composite baryon made of three quarks, like the proton.
• D. Quark: Elementary fermion but interacts via strong force, forming hadrons.

Final answer: C