Question

How many of the following molecules have sp3d2 hybridization on the central atom?
SeCl6 XeF4 IF5 AsCl5

1

2

3

4

Answer 1

3 is correct.
Note:
The first three from the left have sp3d2

Answer 2

A good rule of thumb to remember is that d2sp3 hybridized atoms create six potential orbitals, filled by a combination of single and double bonds or lone pairs.

In SeCl6, the central atom is the selenium atom, bonded to six chlorine atoms, hence exhibiting sp3d2 hybridization.

In XeF4, however, xenon doesn't have two lone pairs. It has four orbitals, all filled with bonds to iron. It is not sp3d2 hybridized.

Both IF5 and AsCl5 exhibit the same geometry and hybridization. The central atom is bonded to five atoms, and there is a lone pair, making six orbitals in total, and sp2d3 hybridization. Here is a lewis-structure of IF5, which will also apply to AsCl5: