Consider the structure of ozone, $O_3$

Ozone has resonance structures: $\ce{O=O-O <-> O-O=O}$

Because of resonance, the two $\ce{O-O}$ bonds become equivalent.

Hence, both bond lengths are equal.

So, A is correct.

Check thermal decomposition of $O_3$

Thermal decomposition: $2\ce{O3(g)} \rightarrow 3\ce{O2(g)}$

Ozone is thermodynamically less stable than oxygen and decomposes to form $\ce{O2}$ with release of heat.

Thus, decomposition is exothermic, not endothermic.

So, B is incorrect.

Magnetic nature of $O_3$

Ozone has all electrons paired in its molecular orbitals, so it is diamagnetic.

Therefore, C is correct.

Shape of $O_3$

In $O_3$, the central oxygen has:

• two bond pairs
• one lone pair

Thus, electron-pair geometry is trigonal planar, but molecular shape is bent (angular).

Therefore, D is correct.

Final selection

Correct statements are: $\boxed{A,\ C,\ D}$

Comparison with stored correct answer

Stored correct answer: $A, C, D$

This matches the derived answer exactly.