Question

A substance in which large energy gap separates the valence and conduction band is a
A. Metal
B. Metalloid
C. Semiconductor
D. Insulator

Answer 1

Valence band and Conduction band are the energy levels separated by some amount of energy. So the higher the energy difference between them, the larger will be the energy gap.

**Complete step by step answer
Definition of Conduction Band:**A conduction band is defined as that energy band that consists of free electrons that are responsible for conduction. Thus this band is named so. Basically the electrons that get moved out from the valence band by experiencing external force reach the higher energy band in order to support conduction.
Definition of Valence Band: It is basically defined as the energy band that comprises valence electrons present in the outermost shell of an atomic structure. These valence electrons, when provided with sufficient energy, get changed into free electrons and move to the conduction band thereby causing conductivity.
So basically energy gaps which separate conduction band and valence band give the information that whether the substance is conductor, insulator or semiconductor.
There are total 3 no. of cases in this situation:
1. When the energy gap between valence band and conduction band is large then it is an insulator.
2. When the energy gap between valence band and conduction band is not large or even small then the substance will be semiconductor.
3.When valence band and conduction band overlap then it will be a conductor.
So this implies that substance in which the large gap separates the valence band and conduction band is Insulator.

**So the correct option is D. Insulator

Additional Information: **
1. Insulator is a substance which does not conduct electricity or a substance in which free electrons are not present.
2. Conductor is a substance which conducts electricity or it is a substance in which free electrons are present.
3. Semiconductor shows properties of conductors as well as of insulators.

Note:
Conduction Bands and Valence Bands are nothing but just bands signifying energy of electrons. Semiconductors have a very small energy gap between valence and conduction band.