Answer:
The correct option is A. O2 is composed of elements and not compounds.
Explanation:
An element can be described as a substance that cannot be broken down into any simpler substance because it is made up of the same type of atoms. The periodic table consists of all the elements that scientists have discovered. For example, the element hydrogen.
On the other hand, a compound can be described as a mixture of two elements. Hence, The options B, C, D are incorrect because each option is a compound.
The option A comprises of two atoms of the same element i.e oxygen. hence, A is the correct option.
