Quark charges sum to +e for π⁺

Steps:

• Recall π⁺ is a meson with charge +e, composed of one quark and one antiquark.
• List quark charges: u = +2/3 e, d = -1/3 e; antiquarks have opposite: ū = -2/3 e, d̄ = +1/3 e.
• Calculate total charge for each option by adding constituent charges.
• Identify the combination yielding +1 e as the π⁺.

Why D is correct:

• D (u d̄) has charge +2/3 e + 1/3 e = +1 e, matching the π⁺ definition as an up quark and anti-down quark meson.

Why the others are wrong:

• A (uud): +2/3 + 2/3 - 1/3 = +1 e, but it's a baryon (three quarks), not a meson like π⁺.
• B (udd): +2/3 - 1/3 - 1/3 = 0, neutral, not +e.
• C (dū): -1/3 - 2/3 = -1 e, negative charge, opposite of π⁺.

Final answer: D