Answer: Option (D) is the correct answer.
Step-by-step explanation:
A nuclear reaction is a reaction in which nucleus of an atom either combines with nucleus of another atom or splits into different nuclei.
For example,

Here, nuclei of carbon on bombardment with a neutrons splits into nuclei of nitrogen and along with that it emits a bets particle (
).
Whereas a physical change is a change in which there occurs no change in chemical composition of a substance. For example, mass, density, boiling point etc.
On the other hand, chemical change is the change that brings change in chemical composition of a substance. Electrons are involved in a chemical change.
A phase is defined as a physical form of a matter. For example, liquid, solid, gas are all phases of matter.
Thus, we can conclude that during nuclear change an atom of carbon become an atom of nitrogen.