Carbon dioxide

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Carbon dioxide (CO₂) is the name of the linear molecule O=C=O. At normal temperature and pressure (NTP) 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 NTP). 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. Lately CO₂ has become notorious as a greenhouse gas.