Q. Which one of the silicon components does not exist?

 2150  217 AMUAMU 2015The p-Block Elements Report Error

Solution:

does not exist because the chlorine atom is much larger atom which does not allow the six chlorines to surround the silicon due to repulsions between chlorine atoms. Silicon cannot accommodate chlorine around it.
Hence, due to inter electron repulsion between chlorine atoms, the compound is unstable and not known.