Which element is a fundamental part of the chemical composition of water?

Water, chemically represented as H₂O, is composed of two hydrogen atoms bonded to one oxygen atom. This unique combination is what makes hydrogen a fundamental part of the chemical composition of water. Without hydrogen, water as we know it would not exist.

Oxygen, while also crucial to the structure of water, is not one of the options listed as the correct answer here. Carbon and nitrogen play important roles in many biological systems and chemical processes but are not components of water itself. Ozone, which consists of three oxygen atoms, is a different molecule entirely and does not relate to the composition of water. Thus, identifying hydrogen as the correct answer highlights its essential role in the formation of water molecules.