Which one of the following compounds of Group-$14$ elements is not known?

Which of the following exhibits moderate electrical conductivity?

Choose the $INCORRECT$ statement.

Carbon can form $p\pi-p\pi$ bond with which kind of elements?

The catenation tendency of $C$,$Si$ and $Ge$ is in the order $Ge < Si < C$. The bond energies (in $kJ \ mol^{-1}$) of $C-C$,$Si-Si$ and $Ge-Ge$ bonds,respectively,are:

Which of the following species does not exist?