What is a resonance structure? Why are resonance structures required? Explain with a suitable example.

(N/A) Resonance Structures: Different Lewis structures of a single molecule or ion are known as resonance structures. According to the concept of resonance, whenever a single Lewis structure cannot describe a molecule accurately, more than one Lewis structure, known as resonance structures, are used to describe it.
Resonance structure of ozone $(O_3)$: To draw resonance structures, the position of the nuclei of the atoms is not changed. In every resonance structure, the position of bonding and non-bonding electrons changes, but the identity of the Lewis structure is not considered different. The different resonance structures are represented by a double-headed arrow. All resonance structures have similar energy.
Two resonance structures of the $O_3$ molecule are $(I)$ and $(II)$, and $(III)$ is the resonance hybrid.
Limitation of resonance: None of the individual structures are seen as the "correct" structure. The $O-O$ single bond length is $148 \ pm$ and the $O=O$ double bond length is $121 \ pm$. Thus, individual single and double bond lengths are not experimentally present in $O_3$.
Therefore, the correct structure of $O_3$ is not $(I)$ or $(II)$.
Resonance: The correct structure is the resonance hybrid. Experimentally determined oxygen-oxygen $(O-O)$ bond lengths in the $O_3$ molecule are the same, $128 \ pm$. So, $(III)$ is the real or accurate structure of $O_3$ in which the single and double bonds are not static. Resonance structures are necessary because they facilitate the determination of the correct molecular structure that a single Lewis structure cannot represent.
Orientation: $A$ single assumed structure cannot give the correct bond length and bond energy.
Advantage: It provides an assumption of the correct structure.