First draw the Lewis Structure of so2.

Note that there are 3 things or regions around the central atom. 1 single bond, 1 double bond and a lone pair.

The hybridization for this is sp2

Where: s has 1 orbital p has 3 orbitals d has 5 orbitals f has 7 orbitals

sp2 s has 1 orbital, p has 2 orbitals = 3 regions

Let’s say you have 4 things or regions around the central atom like nh3

The hybridization for this is sp3

sp3 s has 1 orbital, p has 3 orbitals = 4 regions

Let’s look at PCL5. It has 5 things or regions around the central atom.

The hybridization for this is sp3d

sp3 s has 1 orbital, p has 3 orbitals, d has 1 orbital = 5 regions

We can’t have more than 3 orbitals on p so that’s why we jumped to d orbital.

Don’t forget to check this also