What is the common form of carbonic acid in aqueous solution?

The common form of carbonic acid in aqueous solution is represented by the molecular formula H2CO3. Carbonic acid is formed when carbon dioxide (CO2) dissolves in water. In this reaction, CO2 reacts with water to produce H2CO3, which can further dissociate to produce bicarbonate (HCO3-) and carbonate ions (CO3 2-).

H2CO3 plays a crucial role in maintaining the pH balance in natural waters and biological systems, acting as a weak acid that contributes to buffering. This equilibrium is essential for various environmental and physiological processes, including respiration in living organisms and the regulation of acid-base balance in blood.

In contrast, the other options either represent different substances or forms of carbon that are not the aqueous form of carbonic acid. CO2, while a precursor to H2CO3, is not the acid itself in solution. CH4 is methane, a completely different compound, and CO3 2- is the carbonate ion, which is one of the products of the dissociation of carbonic acid, but not the acid itself in a solution. Thus, H2CO3 is the definitive answer when considering the common form of carbonic acid in aqueous environments.