What is the order of energy gap in a semiconductor?

Why is $\mathrm{Ge}$ preferred over $\mathrm{Si}$ for making semiconductor devices?

Name two impurities that will make pure $\mathrm{Si}$ an extrinsic semiconductor.

Name the charge-carriers at room temperature in a conductor, an intrinsic semiconductor and an insulator.

Are the mobilities of electron and hole equal in a semiconductor?