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carbon dioxide, (CO2), a colourless gas having a faint sharp odour and a sour taste. It is one of the most important greenhouse gases linked to global warming, but it is a minor component of Earth’s atmosphere (about 3 volumes in 10,000), formed in combustion of carbon-containing materials, in fermentation, and in respiration of animals and employed by plants in the photosynthesis of carbohydrates. The presence of the gas in the atmosphere keeps some of...