The correct answer is (b) Decreases with an increase in temperature
Explanation: In the case of an insulator, the energy gap between the conduction band and the valence band is very large. When the temperature is increased, the electrons move from the conduction band to the valence band and hence it starts conducting. When conductance increases, resistance decreases, since C=1/R. Thus, when the temperature increases, resistance decreases in insulators.