Exam-style question
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Which of the following reactions correctly balances charge, baryon number and lepton number?.
- A.p + e⁻ → n + β⁻
- B.p + e⁻ → n + β⁺
- C.p + e⁻ → n + β⁰
- D.p + e⁻ → n + β⁺ + β⁻
Model answer
What a good answer should say
- The reaction p + e⁻ → n + β⁺ conserves all three quantities.
Explanation
Why this works
Initial state: proton (charge +1, baryon 1, lepton 0) + electron (charge –1, baryon 0, lepton +1). Final state: neutron (charge 0, baryon 1, lepton 0) + positron (charge +1, baryon 0, lepton –1).
Charge: +1–1 = 0 = 0+1; baryon: 1+0 = 1+0; lepton: 0+1 = 0–1. All conserved.
Common mistake
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