When the number of hybrid orbitals, H is 4 , the hybridisation is sp3. H=21[ V+M−C+A] where, V= number of valence electrons of central atom MCA= number of monovalent atoms = total positive charge = negative charge (a) For CH4, H=21[4+4−0+0]=4, thus sp3 hybridisation (b) For SF4, H=21[6+4−0+0]=5, thus sp3 d hybridisation (c) For BF4−, H=21[3+4−0+1]=4, thus sp3 hybridisation (d) For NH4+, H=21[5+4−1+0]=4, thus sp3 hybridisation Thus, only in SF4, the central atom does not have sp3 hybridisation