In the energy band diagram of insulators,the band gap and the conduction band are respectively:

Carbon,Silicon,and Germanium atoms have four valence electrons each. Their valence and conduction bands are separated by energy band gaps represented by $(E_g)_C$,$(E_g)_{Si}$,and $(E_g)_{Ge}$ respectively. Which one of the following relationships is true in their case?

The energy gaps $(E_g)$ between the valence band and conduction band for diamond, silicon, and germanium are in the order:

The upper level of the valence band and the lower level of the conduction band overlap in the case of

$C$ and $Si$ both have the same lattice structure,having $4$ bonding electrons in each. However,$C$ is an insulator whereas $Si$ is an intrinsic semiconductor. This is because:

$Sn, C, Si$,and $Ge$ are all group $XIV$ elements. Yet,$Sn$ is a conductor,$C$ is an insulator,while $Si$ and $Ge$ are semiconductors. Why?