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 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