In gamma ray emission from a nucleus:
A) Both, the neutron number and the proton number change
B) There is no change in the proton number and the neutron number
C) Only the neutron number changes
D) Only the proton number changes

Hint: To solve this question, we need to see which product is liberated in a gamma decay. The change in proton number is indicated by the liberation of charged particles, while the neutron number is changed if any kind of particle having mass is liberated.

Complete step-by-step solution:
We know that an atom consists of a nucleus around which several electrons are present in various shells. Like the atom, the nucleus also has different energy levels for the distribution of the nucleons. The protons and the neutrons are well distributed within the nucleus. We know that when an excited electron present in a higher shell returns to a lower shell, then radiation is emitted. The radiation has energy equal to the difference in the energy of the shells. Also, these shells have the energies of the order of electron volts. So the emitted radiation also has the energy of the order of electron volts.
Likewise, a nucleus also gets excited. But here the energy levels are of the order of mega electron volts, due to the strong nuclear forces. So when the nucleus gets de-excited, then it liberates radiation having energy of the order of mega electron volts. So the gamma rays are liberated in the de-excitation of the nucleus. This phenomenon is known as the gamma decay.
Now, in this process no particle is being emitted. Only the gamma radiation is emitted. We know that radiation is an electromagnetic wave which only carries energy with it. No charge or mass is carried by the electromagnetic wave.
So neither the neutron number nor the proton number changes in the gamma emission from a nucleus.
Hence, the correct answer is option (B).

Note
The gamma radiations emitted in a gamma decay are used in the process of irradiation to kill bacteria from foods. They are also used in killing several types of cancer cells.