Which statement is true about electron shells?

• A. Each shell has discrete energy levels
• B. All shells share the same energy level
• C. No energy levels exist in shells
• D. Energy levels vary continuously within a shell

Answer: (A)

Electrons in atoms can only occupy specific, fixed energies—the levels are quantized and organized into shells. This means each shell has discrete energy values rather than a continuous range. In XRF, transitions between these distinct levels produce photons with specific energies, which is why characteristic X-ray lines appear at particular energies.

So, the statement that each shell has discrete energy levels is correct because it reflects the quantized nature of atomic energy states. The other ideas—that shells share the same energy, that there are no energy levels, or that energy varies continuously within a shell—don’t match how atomic structure and emission spectra behave.