The correct statement(s) about O3 is(are): O-O bond lengths are equal; thermal decomposition of O3 is endothermic; O3 is diamagnetic in nature; O3 has a bent structure.

Ozone is diamagnetic in nature (due to presence of paired electron) and both the O – O bond length are equal. It has a bent structure. Ozone decomposes to give oxygen molecules which are more stable than ozone molecules. And if a molecule is more stable than another, then it possesses relatively lesser energy (and hence enthalpy) than that possessed by the less stable one. That is why the decomposition of ozone is an exothermic process. So, (A, C) are correct.