β⁺ Decay Reduces Proton Number and Emits Neutrino

Steps:

• β decay includes β⁺ type, where a proton converts to a neutron in nucleus X (Z protons).
• Daughter nucleus Y thus has Z-1 protons.
• β⁺ decay emits a positron and neutrino; here, W represents the neutrino.
• γ is a photon from possible de-excitation of Y.

Why B is correct:

• In β⁺ decay, proton number decreases to Z-1, and the emitted lepton is a neutrino, matching the equation's W.

Why the others are wrong:

• A: Antineutrino accompanies β⁻ decay, not β⁺.
• C: Z+1 occurs in β⁻ decay, which emits antineutrino.
• D: Z+1 pairs with antineutrino in β⁻ decay, not neutrino.

Final answer: B