Quark composition in hydrogen-3 nucleus

Steps:

• Hydrogen-3 nucleus (tritium) consists of 1 proton and 2 neutrons.
• A proton has quark content uud, containing 1 down quark.
• A neutron has quark content udd, containing 2 down quarks each.
• Total down quarks: 1 (proton) + 4 (2 neutrons) = 5.

Why D is correct:

• Standard quark model defines proton as uud (1 down) and neutron as udd (2 downs), yielding 5 down quarks total in the nucleus.

Why the others are wrong:

• A: Underestimates by ignoring one neutron's down quarks.
• B: Matches total up quarks (2 from proton + 1 per neutron = 3).
• C: Counts total quarks in proton only (3) or miscounts neutrons.

Final answer: D