The formula to find the hybridisation of a molecule is 1/2(G+V) where G is the group number of the central atom and V is the number of monovalent atoms (F,Cl,H,Br only). If it is not among them then V = 0.So, there are 2 cases:
Case i:
If V is one of of the above monovalent atoms then 1/2(G+1)=3 implies G = 5 which means the nitrogen group. Nitrogen after forming the bond must have 2lp which satisfies the above condition but no compound is yet known in the form NX . Case i does not apply.
Case ii:
1/2(G+0)=3 implies G=6. If there is 1bp then there will be more than 2 lp left. Hence case ii does not apply.
Hence proved.
Please approve it if found useful. Any doubts please be free to ask...
