Which of the following is non -existent

Options

A. `AIF_(6)^(3-)`
B. `CoF_(6)^(3-)`
C. `BF_(6)(3-)`
D. `SiF_(6)^(2-)`

Answer

C

Explanation

Maximum covalency of B is only 4 as it does not have d - orbita `(1s^(2) 2s^(2) 2p^(1))`