What is the chemical symbol for water?

The chemical symbol for water is H2O. This notation indicates that each molecule of water is composed of two hydrogen atoms and one oxygen atom. The "H" represents hydrogen, while the "O" represents oxygen, and the subscript "2" signifies that there are two hydrogen atoms bonded to one oxygen atom. This molecular structure is fundamental to the properties of water, which is essential for life on Earth. Understanding this composition is key to many scientific concepts, including biology, chemistry, and environmental science, as water plays a crucial role in various biochemical processes and ecosystems.

The other choices represent different chemical substances: NaCl is the formula for table salt (sodium chloride), CO2 corresponds to carbon dioxide, and O2 denotes molecular oxygen. Each of these has distinct properties and functions, differing from the properties that make water unique.