In terms of band theory, what is the difference (i) between a conductor and an insulator (ii) between a conductor and a semiconductor.

Explanation

(i) In case of same conductors, the valence band is partially filled with electrons and the energy gap between the valence band and the conduction band is very small. In case of same other conductor, valence band is completely filled with electrons and the conduction band overlaps with the valence band and hence, there is no energy gap between these bands.
In case of insulator, the valence band is completely filled with electrons and the energy gap between the valence band and the conduction band is very large.
(ii) In case of some conductors, valence band is partially filled with electrons and the energy gap between the valence band and the conduction band is very small. In case of some other conductors, the valence band is completely filled with electrons and the conduction band overlaps with the valence band and hence, there is no energy gap between these bands.
In case of semiconductor, the valence band is completely filled with electrons and the energy gap between the valence band and the conduction is small but it is greater than that of a conductor and less than of an insulator.