Question

Energy band gap between valence band and conduction band for insulator is:
A. Zero
B. Greater than $9eV$
C. Less than conductors
D. Approximately $1eV$

Answer 1

Hint: The band gap energy between the valence band and the conduction band for a material is the difference between the two energy bands. Insulators are the materials, which have the largest value for the band gap energy.

Complete answer:
First, we will understand what is the forbidden energy gap of a material. According to band theory each material has two energy bands (levels) – valence band and conduction band. Actually, the two bands have different energy levels and the difference between these two energy levels (gap between the two bands) is called the forbidden energy gap.

Initially, the electrons are situated in the valence band with lower energy and when they absorb a particular amount of energy, they excite to a higher energy level i.e. the conduction band. The band gap depends on the value of the forbidden energy for the material. If the forbidden energy is large, then the band gap will be more.

Insulators are the materials, which have the largest value of the forbidden energy. Therefore, the band gap for insulators is largest. This means that insulators need the highest amount of energy for conduction of electrons. Hence, the energy band gap between the valence band and conduction band for the insulator is greater than $9 eV$.

Hence, the correct option is B.

Note:Note that the forbidden energy for an insulator cannot be equal to zero. Hence, option is A is incorrect. Conductors have the least energy band gap. Therefore, the energy band gap for insulators is more than that of conductors. Hence, option C is incorrect.
The band gap energy for is approximately equal to $1 eV$ for semiconductors. Hence, option D is incorrect.