In which of the following pairs , the two species are not isostructural ? `PCl_4^(+)` and `SiCl_4`, `PF_5` and `BrF_5`, `AlF_6^(3-)` and `SF_6`, `CO_3^(2-)` and `NO_3^(-)`

Options

A. `PCl_4^(+)` and `SiCl_4`
B. `PF_5` and `BrF_5`
C. `AlF_6^(3-)` and `SF_6`
D. `CO_3^(2-)` and `NO_3^(-)`

Answer

B

Explanation

`PF_5(sp^3d)` has trigonal bipyramidal geometry while `BrF_5 (sp^3d^2)` has square pyramidal or distorted octahedral geometry. All the remaining have the same structure: `PCl_4^(+), SiCl_4` (tetrahedral,`sp^3 , AlF_6^(3-)` and `SF_6` ) octahedrat, `sp^3d^2` and `CO_3^(2-)` and `NO_3^-` (trigonal planar `sp^2`)