The hybridization of IF5 can be determined by the number of lone pairs around iodine and the number of sigma bonds formed between I and F. Since the central atom iodine has 7 valence electrons out of which 5 electrons form 5 sigma bonds with F atoms and and 2 electrons form 1 lone pair making the stearic number 6 which implies the hybridization of the central atom is sp3d2 where the geometry is octahedral and the shape is square pyramidal.