621.

Which of the following species is not stable?

• [GeCl₆]^2-

• [Sn(OH)₆]^2-

• [SiCl₆]^2-

• [SiF₆]^2-

(i) Due to presence of d-orbital in Si, Ge and Sn they form species like SiF₆^2-, [GeCl₆]^2-, [Sn(OH)₆]^2-.

(ii) SiCl₆^2- does not exist because six large chloride ions cannot be accommodated around Si⁴⁺ due to limitation of its size.