Chemistry Regents Practice Test 2026 – Complete Prep Resource

A nuclear reaction specifically refers to processes that take place within the nucleus of an atom. This can include events such as nuclear fission (where a nucleus splits into smaller parts, releasing energy) or nuclear fusion (where smaller nuclei combine to form a larger nucleus, also releasing energy). These reactions fundamentally alter the identity of the elements involved, changing one type of atom into another through the transformation of protons and neutrons.

In contrast, other processes, like changes in chemical bonds, are characterized as chemical reactions, which occur in the outermost electron shells of atoms without altering the nucleus. While high temperatures can facilitate certain nuclear reactions, temperature alone does not define the reaction itself. Similarly, processes that release energy but do not involve changes to the atomic nuclei are typically classified outside of nuclear reactions. Thus, the definition that highlights changes in an atom's nucleus accurately captures the essence of what a nuclear reaction entails.