X-Rays are ionizing radiation.

• A. They are emitted from the nucleus and non-ionizing.
• B. They are emitted from the electron cloud and ionizing.
• C. They are visible light.
• D. They are infrared.

Answer: (B)

X-rays are a form of electromagnetic radiation energetic enough to ionize matter. This energy typically arises from processes involving electrons in atoms—the electron cloud—not from the nucleus. For example, when an inner-shell vacancy is created and an electron from a higher shell drops to fill it, a photon in the X-ray range is emitted. Fast electrons slowing down in matter (bremsstrahlung) also produce X-rays. Because their photons have enough energy to remove electrons, X-rays are ionizing radiation. The other statements misidentify the source (nucleus) or mix in other parts of the spectrum (visible light or infrared) or non-ionizing radiation. Therefore, X-rays being emitted from the electron cloud and being ionizing best captures their nature.