Q.13. In insulators
A. valence band is empty and conduction band is filled with electrons.
B. conduction band is empty and valence band is completely filled with electrons.
C. valence band is partially filled.
D. conduction band is partially filled with electrons.
Answer :- B. conduction band is empty and valence band is completely filled with electrons.
Explanation :-
The correct answer for the description of electronic bands in insulators is:
Option B: conduction band is empty and valence band is completely filled with electrons.
In insulators, there is a large energy gap between the valence band and the conduction band. The valence band is the band of electron orbitals that electrons occupy at absolute zero temperature, and it’s usually filled with electrons in an insulator. The conduction band is the band above the valence band where an electron may be excited to in order to conduct electricity. In insulators, this conduction band is empty because the energy gap (band gap) between the valence band and the conduction band is so large that electrons in the valence band do not normally have enough energy to jump into the conduction band under room temperatures or normal conditions. Hence, there is no electrical conductivity in insulators under these conditions.
Let’s break down the incorrect options:
Option A: In insulators, the valence band is not empty. It is filled with electrons, which is in direct contradiction to what this option states.
Option C: In insulators, the valence band is completely filled, not partially filled. It is the complete filling of the valence band which contributes to their insulating properties, combined with the large energy gap to the conduction band.
Option D: The conduction band in insulators is not partially filled; it is empty due to the energy required to move electrons from the valence band to the conduction band being prohibitively large for thermal excitation.