Answer: option 1. different molecular structures and different properties.
Step-by-step explanation:
1) O₂ and O₃ are different forms of the same element, in the same physical state (gaseous).
2) That is what is called allotropes.
3) The definition of allotropes is different forms of an element with different structures and different properties in the same physical state.
Graphite and diamond is other example of common allotropes.
4) O₃ and O₂ have the same kind of atoms (oxygen), but they are bonded differently (different structure, one molecule has 3 atoms, other 2 atoms) which conferes them different properties (e.g. different odor, different chemical reactivity).