Class 12 NEET Physics Atoms and Nuclei Part 1

Concept: In beta-plus decay ($\beta^+$ decay), a proton converts into a positron, and a neutrino is emitted to conserve lepton number and energy. Explanation: We need to identify particle $X$ using conservation laws: Step 1: Apply Conservation of Mass Number (A) $$A_{\text{initial}} = A_{\text{final}}$$ $11 = 11 + 0 + A_X$ $A_X = 0$ Step 2: Apply Conservation of Atomic Number (Z) $Z_{\text{initial}} = Z_{\text{final}}$ $6 = 5 + 1 + Z_X$ $Z_X = 0$ Step 3: Identify the particle A particle with mass number $A = 0$ and atomic number $Z = 0$ is a neutrino ($\nu_e$). In $\beta^+$ decay, the emitted neutrino is specifically an electron neutrino (not an anti-neutrino, which is emitted in $\beta^-$ decay). Verification:

• Mass number: $11 = 11 + 0 + 0$ ✓
• Atomic number: $6 = 5 + 1 + 0$ ✓
• Lepton number is conserved ✓

Answer: C. neutrino