Final answer:
The sulfite ion (SO32-) and the sulfate ion (SO3) are best represented by resonance structures, where multiple equivalent forms can illustrate the distribution of electrons around the central atom.
Step-by-step explanation:
The best Lewis structure with a resonance structure from the options provided (SCO, I3-, SO32-, BF3, SO3) can be seen in the sulfite ion (SO32-) and the sulfate ion (SO3). These molecules can be represented by several equivalent resonance forms where the placement of the electrons may vary but the overall structure remains consistent. For example, the sulfite ion will have several forms due to the different possibilities of where the double bonds can be placed between the sulfur and oxygen atoms. Similarly, sulfate ion also has multiple resonance forms depicting the sulfur-oxygen bonds. The carbonate ion (CO32-), as another example, is often drawn as a resonance hybrid, indicating that the double bonds are delocalized over the three oxygen atoms, giving each bond a partial double-bond character.