How are holes produced in a semiconductor?

The band gap in Germanium and Silicon in $eV$ respectively is

Choose the $FALSE$ statement from the following.

Explain the change in the energy band structure of an intrinsic semiconductor with temperature by drawing a figure.

$C$, $Si$ and $Ge$ have the same lattice structure. Why is $C$ an insulator while $Si$ and $Ge$ are intrinsic semiconductors?

Pure sodium $(Na)$ is a good conductor of electricity because the $3s$ and $3p$ atomic bands overlap to form a partially filled conduction band. By contrast,the ionic sodium chloride $(NaCl)$ crystal is: