Pure silicon is an insulator but on heating it becomes a semi-conductor because:
On heating, electrons occupy higher energy states
No effect on electrons on increasing temperature
On heating, electrons move freely in crystals
Both (1) and (3)
Pure silicon has its electrons in a lower energy state. An increase in temperature promotes the electrons to occupy higher energy states. These electrons move freely in crystals and are responsible for electrical conduction.
Therefore, Option(4) is correct.