Answer:
(i) In a conductor, the energy gap between
the valence band and the conduction band is very small and electrons easily
flow into the conduction band. Thus, it conducts electricity. On the other
hand, in an insulator, the energy gap between the top of the valence band and
the bottom of the conduction band is so large that enough energy is not
available under normal conditions to promote the electrons from valence band to
conduction band. The in-between region is called the forbidden zone.
(ii) In conductors, the energy gap between
the valence band and conduction band is very small and electrons easily flow
into the conduction band. Thus, it conducts electricity. On the other hand, in
a semi-conductor, the energy gap between the valence band and the conduction
band is smaller than in insulators but larger than in conductors. The thermal
energy available under ordinary conditions is sufficient to excite some
electrons from valence band to conduction band and thus a small amount of
current can flow through them.
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