Classifying subatomic particles as hadrons or leptons

Steps:

• Hadrons are composite particles made of quarks, subject to the strong nuclear force.
• Protons consist of two up quarks and one down quark (uud), making them hadrons.
• Neutrons consist of one up quark and two down quarks (udd), making them hadrons.
• Electrons are fundamental particles that do not contain quarks and are not affected by the strong force, classifying them as leptons.

Why D is correct:

• Protons and neutrons are baryons (three-quark composites), defined as hadrons; electrons are elementary fermions defined as leptons in the Standard Model.

Why the others are wrong:

• A: Electrons are leptons, not hadrons.
• B: Protons are hadrons, not leptons.
• C: Electrons are leptons, not hadrons; neutrons are hadrons, not leptons.

Final answer: D