Which compound is known by the chemical formula CO₂?

The compound known by the chemical formula CO₂ is carbon dioxide. Each molecule contains one carbon atom covalently bonded to two oxygen atoms, and the gas is colorless at ordinary concentrations.

Carbon dioxide is produced by respiration, combustion, volcanic activity, and the decomposition of organic matter. Plants, algae, and some bacteria use it in photosynthesis, converting carbon dioxide and water into energy-rich organic compounds while releasing oxygen.

The gas absorbs infrared radiation, so it is a greenhouse gas. Human activities, especially burning fossil fuels and changing land use, have increased atmospheric carbon dioxide concentrations since the Industrial Revolution. Carbon dioxide is also dissolved in oceans and freshwater, where it participates in acid-base equilibria.

Carbon dioxide should not be confused with carbon monoxide, CO. Carbon monoxide has one oxygen atom and is a highly poisonous gas because it interferes with oxygen transport in blood. Carbon dioxide is also the gas used to carbonate many beverages.