Introduction:
Conductors, insulators, and semiconductors are three different types of materials based on their ability to conduct electricity. The main distinguishing property among these materials is the energy band gap.

Conductors:
- Conductors are materials that allow the flow of electric current easily.
- These materials have a high number of free electrons available for conduction.
- Free electron charges are one of the distinguishing properties of conductors.
- In a conductor, the valence band and the conduction band overlap, so there is no energy band gap.
- Due to the overlapping bands, the electrons can easily move from the valence band to the conduction band, resulting in the flow of electric current.

Insulators:
- Insulators are materials that do not allow the flow of electric current easily.
- These materials have a very low number of free electrons available for conduction.
- Insulators have a large energy band gap, which means the energy required for electrons to jump from the valence band to the conduction band is high.
- Due to this large energy band gap, the electrons are tightly bound to their atoms and cannot move freely, thus preventing the flow of electric current.

Semiconductors:
- Semiconductors are materials that have properties between conductors and insulators.
- These materials have a moderate number of free electrons available for conduction.
- The Fermi level after doping is a property that distinguishes semiconductors.
- Doping refers to the intentional introduction of impurities into a semiconductor to modify its electrical properties.
- By doping, the Fermi level can be adjusted, which affects the conductivity of the material.
- Semiconductors have a small energy band gap, which means the energy required for electrons to jump from the valence band to the conduction band is relatively low.
- At room temperature, some electrons can acquire enough energy to cross the energy band gap and contribute to the conduction of electricity.
- The conductivity of semiconductors can be increased by adding impurities with extra electrons (n-type doping) or with missing electrons (p-type doping).

Conclusion:
The energy band gap is the property that distinguishes conductors, insulators, and semiconductors. Conductors have no energy band gap, insulators have a large energy band gap, and semiconductors have a small energy band gap. While free electron charges and Fermi level after doping are also relevant properties, they do not specifically distinguish between the three material types.