Beta-Plus Decay Changes Atomic Number

Steps:

• Identify initial and final nuclei: ²⁴Mg (Z=12, A=24) decays to ²⁴Na (Z=11, A=24).
• Note mass number A remains 24, so no alpha or fission; atomic number Z decreases by 1.
• Recall β⁺ decay converts proton to neutron, reducing Z by 1 while keeping A constant.
• In β⁺ decay, emitted particles are positron (β⁺) and electron neutrino (ν_e).

Why B is correct:

• β⁺ decay follows p → n + β⁺ + ν_e, matching Z decrease and particle emission.

Why the others are wrong:

• A: β⁻ decay increases Z by 1 (n → p + β⁻ + ν̄_e), opposite effect.
• C: β⁺ decay emits neutrino, not antineutrino (which pairs with β⁻).
• D: γ (photon) and neutrino change neither Z nor A; no transmutation to Na.

Final answer: B