Final answer:
Reaction D, which maintains the atomic number of elements, is identified as a chemical reaction because it involves the rearrangement of atoms through bonding without altering the atomic number.
Step-by-step explanation:
When evaluating the statements listed by the student, we must consider the characteristic features of both chemical and nuclear reactions. Statement D indicates that the atomic number of elements remains the same, which is typical of a chemical reaction. As such, the identity of Reaction D is that it is a chemical reaction, because the process involves a rearrangement of atoms through bonding, without altering the atomic number. In contrast, a nuclear reaction involves changes in the atom's nucleus, which can result in a change of the atomic number and often produces a different element.