Question

The free electron gas theory explains conduction in

• A. metals only
• B. semiconductors only
• C. insulators only
• D. all of these

Answer 1

The correct option is A metals only

Free electron gas theory assumes the positive ion cores are embedded in the gas of negative free electrons. The free electrons do not attach permanently with any of the core, hence always free to move through whole crystal.
The large number of free electrons are present only in metals since valence electrons detach from atom easily at room temperature also. In semiconductors large number of electrons are shared by the atoms hence, less number of free electrons are available as compared to the metals. In insulators electrons are tightly bound with the atoms hence negligible(nearly zero) electrons are free.
Hence, the free electron gas theory explains conduction in metals only since large number of free electrons are available for conduction (as per the assumption of model).