What is the chemical formula for water?

Water is a compound made up of two hydrogen atoms covalently bonded to one oxygen atom. This specific ratio of hydrogen to oxygen is what gives water its chemical formula, which is H2O. The "H" represents hydrogen and the "O" represents oxygen; the subscript '2' next to hydrogen indicates that there are two hydrogen atoms in each molecule of water. This unique structure allows water to exhibit essential properties, such as being a universal solvent and having a high specific heat capacity, making it crucial for life on Earth.

Options like CO2, NaCl, and O2 represent different substances. CO2 is carbon dioxide, a gas composed of one carbon atom and two oxygen atoms. NaCl is sodium chloride, commonly known as table salt, made of sodium and chlorine ions. O2 is diatomic oxygen, which consists of two oxygen atoms and is the form of oxygen that is essential for respiration in many living organisms. Each of these compounds serves different roles and possesses distinct properties compared to water.