Basically, the stronger the bond, the shorter the length. A single bond has a longer length than a triple bond. This is because the electron density in the triple bond is greater than a single bond, and "pulls" the atoms closer together. As you probably know, a covalent bond shares electrons and all three of these molecules have covalent bonds. The important things to remember here are resonance structures. take O3 for example. It looks like this O-O=O, with a positive charge on the center oxygen. but it also has the resonance structure, O=O-O. the electrons from the double bond "moved" over to the single, making that one the new double bond. This happens incredibly fast, over and over again, so in actuality all the bonds are 1 and 1/2. Knowing this, I'd say O3 would have the shortest bond length, as both O2 and H2O2 don't have resonance and contain only single bonds. I would say that O2 has the longest bond length, as H2O2 is very stable.
· 10 years ago