Characteristic x-rays are named for the property that is unique to each element. Which property is this?

• A. Frequency
• B. Energy
• C. Intensity
• D. Wavelength

Answer: (B)

Characteristic X-ray energies are fixed values for each element because they come from specific energy differences between atomic shells. This energy acts as a fingerprint: it uniquely identifies the element because the shell spacings depend on the element’s nuclear charge and electron structure. Frequency and wavelength are just alternate ways to express the same photon energy (via E = hν and E = hc/λ), so they are not the primary distinguishing property. Intensity varies with measurement conditions and sample, not with the element’s identity. So the energy of the characteristic X-ray is the property that uniquely identifies the element.