Leptons are fundamental fermions excluding those in the quark family

Steps:

• Recall that leptons are elementary particles including electrons, muons, taus, and their neutrinos, which do not participate in the strong nuclear force.
• Identify the neutron as a composite particle made of three quarks (udd), classifying it as a baryon and hadron.
• Confirm electrons and positrons as charged leptons, and neutrinos as neutral leptons.
• Eliminate options A, B, and D as they fit the lepton definition, leaving C as the non-lepton.

Why C is correct:

• The neutron is a baryon composed of up and down quarks, subject to the strong nuclear force, per the Standard Model classification of hadrons.

Why the others are wrong:

• A: The electron is a fundamental charged lepton.
• B: The neutrino is a fundamental neutral lepton.
• D: The positron is the antiparticle of the electron, thus a lepton.

Final answer: C