Which of the following is classified as a chemical compound?

Water is classified as a chemical compound because it is composed of two different types of atoms, specifically hydrogen and oxygen, that are chemically bonded together. The chemical formula for water, H2O, indicates that each molecule consists of two hydrogen atoms covalently bonded to one oxygen atom. This distinct combination and bonding of elements to form a new substance with unique properties is what defines a chemical compound.

In contrast, salt, while it is also a compound (specifically sodium chloride, NaCl), is often considered in a broader context alongside elements, which could lead to ambiguity in classification when considering the nature of chemical compounds. Oxygen exists as a diatomic molecule (O2), meaning it is made up of two identical atoms of the same element, so it is classified as an element rather than a compound. Gold is an elemental substance composed solely of gold atoms, making it an element as well. Thus, water is the definitive example of a chemical compound in this context.