Which one of the following has smallest energy gap:

Explanation

CONCEPT:Conductor: The material that allows the electric current to flow through them easily is called a conductor.Example: Metals like -iron, silver, copper, etc.Insulator: The material that doesn't allow the electric current to flow through them is called an insulator.Example: Rubber, wood, etc.Semiconductor: The material having an electric current conducting tendency between conductor and insulator is called a semiconductor.Example: Silicon, germanium, etc.Valence band: The region in which the valence electrons of the atom move is called the valence band.Conduction band: The region in which free electrons remain is called the conduction band.Band Gap: The distance between the valence band of electrons and the conduction band of electrons is known as bandgap.It represents the minimum energy that is required to excite an electron up in the valance band to a state in the conduction band where it can participate in conduction.Conductors have the least band gap while insulators have maximum. Semiconductors have a bandgap between conductors and insulators.EXPLANATION:Insulators have the highest bandgapof order 6eV (- 6eV) or more.Semi-Conductors have a bandgap of the order of 1 eV. Conductors have no energy gap (least energy bandgap).This is the reason, they have high conductivity because electrons can move easily from the valance band to the conduction band.So the correct answer is option A.