CBSE Class 12-science Answered

Valence band 

• In solids, the valence band is the highest range of electron energies in which electrons are normally present at absolute zero temperature.
• It is that range of electron energy where electrical conduction is not possible. 
• Electrons with this much energy is bound into the atomic structure of the material, and are unavailable to conduct an electrical current.

Conduction band 

• The conduction band quantifies the range of energy required to free an electron from its bond to an atom. Once freed from this bond, the electron becomes a 'delocalized electron', moving freely within the atomic lattice of the material to which the atom belongs.
• The lowest unfilled energy formed just above the valance band is called conduction band.
• Conduction band is that range of electron energy where electrical conduction is possible.
• Electrons with this much energy is free of their parent atoms, and can move through the medium in which they exist.