The band having lower energy than conduction band is the valence band.
The electrons in valence band are not free to move because they are tightly
bound to the respective nuclei.
The highest energy band formed by the interaction of the outermost energy
levels of closely spaced atoms in solids is called the conduction band.
The conduction band may be partially occupied or vacant.
Electrons in the conduction band are mobile and delocalized over the entire
solid. They conduct electricity when an electrical potential is applied.