It is difficult to find hybridization of complex ions with this formula. so it is easy to find by using below formula1/2{No:of valence electron in central atom+ Monovalent atom attached to central metal atom+anionic charge-cationic charge}
Example NH3
Central atom valence electron is 5
Monovalent Hydrogen atom is 3
cationic or anionic charge is 0
then 1/2(5+3)=4,which says NH3 is sp3 hybridized