Which of the following statements best describes the difference between the valence band and the conduction band in a solid?

• A. The valence band and conduction band are identical and have no energy gap between them in all materials.
• B. The valence band is the highest range of electron energies where electrons are normally present at absolute zero, while the conduction band is the range of energies higher than the valence band where electrons are free to move and conduct electricity.
• C. The valence band contains only protons, while the conduction band contains only neutrons.
• D. The valence band is always empty, while the conduction band is always completely filled with electrons.

Answer: (B)

Verified step by step guidance

1. Understand that in solid-state physics, electrons occupy energy levels grouped into bands rather than discrete levels as in isolated atoms.
2. Recognize that the valence band is the highest energy band that is normally filled with electrons at absolute zero temperature; these electrons are bound to atoms and do not contribute to electrical conductivity.
3. Know that the conduction band is the energy band immediately above the valence band, which is typically empty at absolute zero but can be occupied by electrons when they gain enough energy.
4. Realize that electrons in the conduction band are free to move throughout the solid, allowing them to conduct electric current.
5. Note that the energy gap between the valence band and conduction band (called the band gap) determines the electrical properties of the material, such as whether it behaves as a conductor, semiconductor, or insulator.