Which of the following is the smallest unit of water that retains the composition and chemical properties of the compound?

A proton is a subatomic particle found in the nucleus of an atom and is not capable of existing independently as a unit of water. While protons are crucial for forming atoms, they do not represent the smallest unit of water that retains its chemical identity.

An atom is the basic unit of a chemical element and consists of protons, neutrons, and electrons. However, a single atom of hydrogen or oxygen does not have the properties of water; it is only when these atoms bond together into a molecule that the characteristics of water emerge.

An element refers to a pure substance that cannot be broken down into simpler substances. While water is composed of elements (hydrogen and oxygen), referring to an element does not capture the specific structure needed to maintain the properties of water. An element alone does not retain the unique properties that arise from the combination of its constituent atoms in a molecule.