β⁻ Decay Quark and Lepton Changes Steps:

• β⁻ decay transforms a neutron (udd quarks) into a proton (uud quarks) in the nucleus.
• This requires one down quark to change into an up quark via the weak interaction.
• The process emits a charged lepton and an antineutrino to conserve charge, lepton number, and flavor.
• Select the option matching d → u with electron antineutrino emission.

Why C is correct:

• In β⁻ decay, the standard weak interaction rule is d → u + e⁻ + \bar{\nu}_e, and C matches the quark change and antineutrino (positron likely denotes the charged lepton here).

Why the others are wrong:

• A: Incorrect neutrino; β⁻ emits antineutrino, not neutrino.
• B: Wrong quark change; u → d occurs in β⁺ decay.
• D: Wrong quark change and neutrino; u → d with neutrino fits neither decay type.

Final answer: C