Explanation:

Molecule:

An atom is the smallest particle of an element that takes part in a chemical reaction. It is extremely small in size and cannot be seen even under the most powerful optical microscope. An atom consists of three sub-atomic particles or fundamental particles.

A molecule is an electrically neutral group of two or more atoms chemically bonded together. It is the smallest particle of a substance, which has the properties of that substance and can exist in a free state.