Incorrect Statement on Particle Composition

Steps:

• Define meson as a hadron composed of one quark and one antiquark.
• Identify baryons as hadrons made of three quarks, including the proton.
• Confirm quarks as fundamental particles without internal structure.
• Note the six quark flavors: up, down, charm, strange, top, bottom.

Why A is correct:

• Mesons consist of a quark-antiquark pair, not three quarks, per the quark model of hadrons.

Why the others are wrong:

• B: Protons consist of three quarks (uud), classifying them as baryons.
• C: Quarks are elementary particles in the Standard Model.
• D: The Standard Model defines exactly six quark flavors.

Final answer: A