In terms of band theory, what is the difference between
a. a condcutor and an insulator
b. a conductor and a semiconductor

Explanation

(i) The energy gap between the valence band and conduction band in an insulator is very large whereas in a conductor, the energy gap is very small or there is overlapping between valence band and conduction band.
(ii) In a conductor, there is very small energy gap or there is overlapping between valence band and conduction band but in a semiconductor there is always a small energy gap between them.