Answer: Option (d) is the correct answer.
Step-by-step explanation:
Transmutation is a process which brings changes in the nucleus occur because of change in the number of protons of an atom. Therefore, the atom formed will have different properties from its parent atom.
For example,

A transmutation can be natural or artificial in nature.
Thus, we can conclude that a transmutation reaction must always involve a change in the number of protons in a nucleus of an atom.