Formula of finding hybridisation of a compound??

Hybridisation of a molecule or an ion can be predicted by making  use of the following formula.

Number of Hybrid orbitals (H)=n

=1/2[group no central atom +no of atoms attached to central metal atom (like H , Cl, F.except O) + magnitude of negative charge - magnitude of positive charge]

  For example,

  BeF₂:  H=1/2[2 + 2 -0 + 0] = 2 ; Hybridisation : sp

   CH₄:  H = 1/2[4 + 4 – 0 +0] =4  ; Hybridisation : sp³

  BF₃:  H= 1/2[3 + 3 -0 + 0] = 3  ; Hybridisation : sp²

  SF₆:  H= 1/2[6+ 6 - 0 + 0] = 6  ;  Hybridisation: sp³d²

  PCl₅:  H=1/2[5+5 – 0 + 0] = 5 ; Hybridisation: sp³d

   NH₄⁺:  H= 1/2[ 5+ 4 – 1 +0] = 4 ; Hybridisation =sp³

  CO₃^2-: H=1/2[4+ 0 -0 +2] = 3 ; Hybridisation = sp²

  NO₃^-:  H=1/2[5 + 0 -0+1] =3; Hybridisation = sp²

  The above formula cannot be used for predicting hybridisation state of complex ions.