Which of the following species are not known ?

Options

A. ` [SiCl_6 ]^(2-)`
B. `[CF_6]^(2-)`
C. `[PbCl_6]^(2-)`
D. `[SiF_6]^(2-)`

Answer

B, D

Explanation

Due to the absence of vacant d-orbital in its valenrc shell, carbon cannot expand its coordinatyion number beyond four , hence `[ CF_6 ]^(2-)` is not known. Due to inert pair effect `Pb^(2+)` compounds are highly unstable and gets reduced to `Pb^(4+)` compounds are highly ustabnle and gets reduced to `pb^(2+)` compounds .