Amongst the following the total number of species which does/do not exist is : `SF_6,BF_6^(3-), SF_4, OF_4, AIF_6^(3-),PH_5, PCl_5, NCl_5, SCl_6`

Correct Answer - 5
(1)Amongst hexahalides of sulphur , only `SF_6` is exceptionally stable for steric reason.In `SCl_6`, smaller S cannot accommodate six larger `Cl^(-)` ions.
(2)`PH_5` does not exist as there is large difference in the energies of s,p and d orbitals of P and hence it does not undergo `sp^3d` hybridisation.
(3)`NCl_5` does not exist as there is no d-orbitals with N.
(4)`BF_6^(3-)` does not exist as there is no vacant d-orbitals in B and hence it cannot exceed its covalency beyond four.
(5)Oxygen cannot exceed its covalency as it does not have d-orbital.