Middle School Academic Team Practice Test

The chemical symbol for water is H2O, which represents two hydrogen atoms bonded to one oxygen atom. This formula illustrates the composition of water molecules, highlighting that each molecule contains two hydrogen atoms for every one oxygen atom. Water is a vital substance for life on Earth and is involved in various biological processes and chemical reactions.

In contrast, the other choices represent different chemical compounds: CO2 is the symbol for carbon dioxide, O2 stands for molecular oxygen, and NaCl is the symbol for sodium chloride, commonly known as table salt. Each of these compounds serves different purposes and has distinct properties, highlighting the importance of understanding chemical symbols and formulae in chemistry.