What is the chemical formula for carbonic acid?

Carbonic acid is formed when carbon dioxide dissolves in water. The chemical structure of carbonic acid is represented by the formula H2CO3, indicating that it contains two hydrogen atoms, one carbon atom, and three oxygen atoms. This formula highlights the presence of the hydroxyl groups (–OH) and the carbonyl group (C=O) that define the chemical nature of carbonic acid.

In the context of the other options, water (H2O) does not represent carbonic acid, and carbon dioxide (CO2) is the gas that reacts with water to form carbonic acid, but alone is not the acid itself. The bicarbonate ion (HCO3-) is an anion derived from carbonic acid, and while it is related, it is not the complete formula for carbonic acid. Thus, H2CO3 accurately identifies carbonic acid and reflects its composition.