Answer:
SO3 is a nonpolar molecule and SO2 is a polar molecule.
Step-by-step explanation:
As can be seen in the attached, the SO3 molecule has a trigonal planar geometry. Each individual double bond of S=O is polar but the molecule has symmetrical geometry so the dipole momentums are canceled.
On the other hand, the SO2 molecule has a trigonal planar electron geometry but an angular molecular geometry due to the unbound electron pair. This unbound electron pair creates a total dipole momentum with negative density over the electron pair.