Assertion : The resistivity of a semiconductor increases with temperature. Reason : The atoms of a semiconductor vibrate with larger amplitude at higher temperatures thereby increasing its resistivity.

Step-by-step solution

With the increase of temperature, the average energy exchanged in a collision increases and so more valence electrons can cross the energy gap, thereby increasing the electron-hole pairs. As in a semiconductor, conduction occurs mainly through electron-hole pairs, so conductivity increases with increase of temperature. Which in turn implies that the resistivity of a semiconductor decreases with rise in temperature.