Carbon dioxide

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Carbon dioxide (CO₂) is the name of the linear molecule O=C=O, composed of one carbon atom and two oxygen atoms. At normal temperature and pressure, it is a colorless, almost odorless gas, which is 50% heavier than air. The gas is formed by the combustion of carbon-containing fuels, such as coal, wood, and petroleum. Carbon dioxide itself neither burns nor supports combustion. The gas is very soluble in water (1.45 g/liter at normal temperature and pressure). The solution is weakly acidic—carbonic acid is formed—and therefore CO₂ is sometimes called carbonic acid gas. It is the gas that gives the sparkle to many soft drinks, some wines, and beer. The carbon dioxide gas freezes at −78.5 °C (−109.3 °F) and the frozen form is known as dry ice.

CO₂ has become notorious as a greenhouse gas, helping trap solar radiation in the Earth's atmosphere and gradually warming the climate of the planet, as its concentration has been increasing because of greenhouse gas emissions from fossil fuels and other sources since the beginning of the Industrial Revolution.