In β^- decay, an electron is emitted. It originates from

The correct answer is Option (1) → decay of a neutron from the nucleus

There are no free electrons inside a nucleus. In \( \beta^{-} \) decay a neutron inside the nucleus changes into a proton, and the electron (with an antineutrino) is created in that process and emitted.

    \( \displaystyle n \rightarrow p + e^{-} + \bar{\nu} \)

The proton stays in the nucleus, so Z increases by 1 while A is unchanged.

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic was removed from the latest NCERT book (2026-27), and it also appears to be out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Beta Decay – “… In beta-minus decay, a neutron transforms into a proton within the nucleus according to

    \( \displaystyle n \rightarrow p + e^{-} + \bar{\nu} \qquad (13.24) \)

whereas in beta-plus decay, a proton transforms into neutron (inside the nucleus) via

    \( \displaystyle p \rightarrow n + e^{+} + \nu \qquad (13.25) \)

These processes show why the mass number \( A \) of a nuclide undergoing beta decay does not change; one of its constituent nucleons simply changes its character according to Eq. (13.24) or (13.25).”