In gamma ray emission from a nucleus.

The correct answer is Option (3) → There is no change in the proton number and the neutron number

A nucleus left in an excited state after an alpha or beta decay comes down to a lower energy level by emitting a gamma-ray photon. A photon carries no charge and no mass number, so the nucleus keeps all its protons and neutrons.

    \( \displaystyle {}^{A}_{Z}\mathrm{X}^{*} \rightarrow {}^{A}_{Z}\mathrm{X} + \gamma \)

Option (3) There is no change in the proton number and the neutron number — Correct. Only the energy of the nucleus falls; \( Z \) and \( A \) stay the same, so the proton and neutron numbers do not change.

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):
Gamma Decay – “There are energy levels in a nucleus, just like there are energy levels in atoms. When a nucleus is in an excited state, it can make a transition to a lower energy state by the emission of electromagnetic radiation. … The daughter nucleus reaches the ground state by a single transition or sometimes by successive transitions by emitting one or more gamma rays.”