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

(N/A) $(i)$ In the structure of $Sn$,the valence band and conduction band overlap,meaning the energy gap between them is zero; hence,$Sn$ acts as a conductor.
$(ii)$ In the structure of $C$ (diamond),the energy gap is $5.4 \ eV$,which is quite large,preventing electron excitation to the conduction band; hence,it acts as an insulator.
$(iii)$ The energy gaps in $Si$ and $Ge$ are $1.1 \ eV$ and $0.7 \ eV$,respectively. These gaps are moderate,allowing some electrons to jump to the conduction band at room temperature,making them semiconductors.