$[{SiF}_{6}]^{2 -}$ is known where as ${[{SiCl}_{6}]}^{2 -}$ does not exist because
I) Six large chloride ions cannot be accommodated around ${Si}^{4 +}$
II) Ineraction between lone pair of chloride ion and ${Si}^{4 +}$ is not very strong
III)Silicon is less electronegative than chlorine
IV) ${Si}^{4 +}$ and ${Cl}^{-}$ ions have same size

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An Intiative by Sri Chaitanya

I and IV are correct

II and III are correct

I and II are correct

III and IV are correct

answer is B.

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Detailed Solution

${[{SiF}_{6}]}^{2 -}$ is known where as ${[{SiCl}_{6}]}^{2 -}$ does not exist because the chlorine atom is much larger than fluorine, which does not allow the six chlorines to surround the silicon due to repulsions between chlorine atoms. Silicon cannot accommodate 6 chlorines around it.