In the energy band diagram of insulators,the band gap and the conduction band are respectively:

Assertion $(A)$: When a wire of aluminium and another wire of silicon are heated from room temperature to $80^{\circ} C$,the conductivity of aluminium decreases and that of silicon increases.
Reason $(R)$: Aluminium has a positive temperature coefficient of resistivity and silicon has a negative temperature coefficient of resistivity.

What type of semiconductor is $CdS$?

In which of the following is an ionic bond present?

GaAs is

The state of the energy gained by valence electrons when the temperature is raised or when an electric field is applied is called as: