Which electron shell has the highest energy level?

• A. The outermost shell.
• B. The shell located farthest from the nucleus.
• C. The shell located closest to the nucleus.
• D. Any shell can have the highest energy depending on the atom.

Answer: (C)

The energy of an electron in an atom increases with distance from the nucleus. Electrons closer to the nucleus are more tightly bound (lower energy, more negative binding energy), while those farther out feel less attraction due to shielding by inner electrons and sit at higher energy levels. In a simple hydrogen-like picture, energy depends on the principal quantum number n, so larger n means higher energy. In multi-electron atoms, the outermost shell is still the least tightly bound, and thus has the highest energy. So the outermost shell is the highest energy level. The shell closest to the nucleus is the most tightly bound, not the highest energy.