Choose the correct basic nuclear process underlying \( \beta^{-} \) decay from the following:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( n \rightarrow p + e^{-} + \bar{\nu} \)
In \( \beta^{-} \) decay the nucleus emits an electron, so inside the nucleus a neutron changes into a proton, with an electron and an antineutrino. The charge is conserved (0 on the left; \( +e - e = 0 \) on the right), and so is the lepton number (the electron is +1 and the antineutrino is −1).
Why the other options are incorrect
Option (1) \( n \rightarrow p + e^{+} + \nu \) — Incorrect. The charge is not conserved: 0 on the left and \( +2e \) on the right.
Option (3) \( p \rightarrow n + e^{+} + \nu \) — Incorrect. This conserves charge, but it is the process of \( \beta^{+} \) (positron) decay, not \( \beta^{-} \) decay.
Option (4) \( p \rightarrow n + e^{-} + \nu \) — Incorrect. The charge is not conserved: \( +e \) on the left and \( -e \) on the right.
NCERT (2026-27):
Atomic Masses and Composition of Nucleus – “… A free neutron, unlike a free proton, is unstable. It decays into a proton, an electron and a antineutrino (another elementary particle), and has a mean life of about 1000s.”