What is the chemical formula for water?

Water is a chemical compound formed from two hydrogen atoms and one oxygen atom, which is why its chemical formula is represented as H2O. This reflects the molecular composition of water: the "H" stands for hydrogen, and the "O" stands for oxygen. The subscript "2" indicates that there are two hydrogen atoms for every one oxygen atom in a water molecule.

Understanding the structure of water is essential because it highlights its properties, such as being a solvent for various substances, its ability to regulate temperature, and its fundamental role in biological processes. Other options like CO2 refer to carbon dioxide, which consists of one carbon and two oxygen atoms, while O2 indicates molecular oxygen, composed of two oxygen atoms, and HO2 represents a different and less common molecule known as hydrogen peroxide. None of these correctly describes water, reinforcing the correctness of H2O as the formula for water.