Quark-level process of β⁻ decay

Steps:

• β⁻ decay converts a neutron (udd) to a proton (uud), changing one d quark to u quark via weak interaction.
• This emits e⁻ and ν (electron neutrino, as defined).
• The basic equation is d → u + e⁻ + ν, conserving charge, lepton number, and baryon number.
• Match this to choices: only C fits exactly.

Why C is correct:

• It follows the standard weak force equation for d quark decay in β⁻ process, per the electroweak theory.

Why the others are wrong:

• A: Uses ν̅ (antineutrino), contradicting the key's definition of ν as neutrino.
• B: Shows neutron (ddu) decaying to u + π⁻ + ν, which describes pion emission, not pure β⁻ decay.
• D: Depicts proton (uud) changing to d + π⁺ + ν, resembling β⁺ decay or unrelated strong process.

Final answer: C