Carbon dioxide is a colorless gas with a density about 60% higher than that of dry air. Carbon dioxide (chemical formula CO 2) is a colorless gas with a density about 60% higher than that of dry air. Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. Carbon dioxide, a colorless gas having a faint sharp odor and a sour taste. US carbon dioxide supply is a bottleneck for Covid-19 vaccines. Carbon dioxide (CO2) is an important heat-trapping (greenhouse) gas, which is released through human activities such as deforestation and burning fossil fuels,.