X-rays are produced when which of the following occurs?

• A. A nucleus fissions
• B. A proton decays
• C. An orbital electron changes levels
• D. A neutron is captured

Answer: (C)

X-rays come from changes in the energy levels of electrons within an atom. When an inner-shell vacancy is created, an electron from a higher shell drops into that vacancy. The energy released in this electronic transition falls in the X-ray range, producing a photon (a characteristic X-ray with energy tied to the specific atom). This mechanism is distinct from nuclear processes, which emit radiation (like gamma rays) from changes in the nucleus rather than from electron transitions. So an orbital electron changing levels is the correct explanation for X-ray emission in this context.