What type of semiconductor is $CdS$?

State the conductivity of metals and resistivity of insulators.

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.

In the case of a semiconductor,which of the following statements is wrong?

The intrinsic semiconductor becomes an insulator at

What is the band gap energy for an insulator in $eV$?