Ozone ($O_3$) exhibits resonance between two equivalent structures.

• Bond Order: The actual $O-O$ bond is a partial double bond with a bond order of approximately $1.5$.
• Comparison:
• $O_2$ (Dioxygen): Double bond (Bond Order = $2.0$).
• $O_2^{2-}$ (Peroxide): Single bond (Bond Order = $1.0$).
• Ozone: Since its bond order ($1.5$) is between $1$ and $2$, its bond length is intermediate between the short double bond in $O_2$ and the long single bond in $O_2^{2-}$.