JEE Main 2025 Jan 28 Shift 1, Physics Q12: Radioactivity

JEE Main2025Jan 28, Shift 1Physics

Choose the correct nuclear process from the below options

[p: proton, n: neutron, $e^{-}$ : electron, $e^{+}$ : positron, $ν$ : neutrino, $\overset{ν}{ˉ}$ : antineutrino]

A
$n \to p + e^{-} + \overset{ν}{ˉ}$
B
$n \to p + e^{-} + ν$
C
$n \to p + e^{+} + \overset{ν}{ˉ}$
D
$n \to p + e^{+} + ν$

Solution

A free neutron undergoes $β^{-}$ decay: a down quark converts to an up quark via the weak interaction, emitting a $W^{-}$ boson which decays into an electron and an electron antineutrino.

Charge conservation: $0 = + 1 + (- 1) + 0$ . ✓
Lepton number conservation: $0 = 0 + (+ 1) + (- 1)$ (the antineutrino has lepton number $- 1$ , balancing the electron). ✓

The correct process is $n \to p + e^{-} + \overset{ν}{ˉ}$ .

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JEE Main 2025 Jan 28 Shift 1, Physics Q12: Radioactivity

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