Final answer:
Oxygen and ozone are allotropes, which are different forms of the same element in the same physical state. The conversion from oxygen to ozone is an endothermic reaction requiring energy from electrical discharge or other sources. The correct option is 3.
Step-by-step explanation:
Oxygen and ozone are indeed the same element, but they exist in two different molecular forms. This phenomenon is known as allotropy, which describes the existence of two or more different forms of an element in the same physical state.
While oxygen (O2) is diatomic, ozone (O3) is a triatomic molecule. The process of converting oxygen to ozone is an endothermic reaction, requiring an input of energy that can come from electrical discharge, heat, or ultraviolet light.
It's important not to confuse allotropes with isomers, which are different chemical species that have the same chemical formula but differ in the connectivity or spatial orientation of atoms.
Examples of isomers include geometric isomers like the cis and trans forms of the [Co(NH3)4Cl2]+ ion. Allotropes, on the other hand, can have different physical and chemical properties despite being composed of the same element. The correct option is 3.