The correct answer is: B. Molecular oxygen (O2)
Molecular oxygen (O2) is not believed to be responsible for enhancing the earth’s greenhouse effect. This is because O2 is a very stable molecule and does not absorb infrared radiation. The other gases listed, CFCs, N2O, CO2, and CH4, are all greenhouse gases that absorb infrared radiation and contribute to the greenhouse effect.
Chlorofluorocarbons (CFCs) are man-made chemicals that were once widely used in refrigerants, aerosol propellants, and foam-blowing agents. CFCs are very stable and do not break down in the atmosphere. They can reach the stratosphere, where they break down and release chlorine atoms. These chlorine atoms react with ozone molecules, destroying them. Ozone is a gas in the stratosphere that absorbs harmful ultraviolet radiation from the sun. The destruction of ozone has led to an increase in the amount of ultraviolet radiation reaching the Earth’s surface, which has increased the risk of skin cancer and other health problems.
Nitrous oxide (N2O) is a greenhouse gas that is produced by natural processes such as soil cultivation, animal waste, and the burning of fossil fuels. N2O is also produced by human activities such as the use of nitrogen fertilizers and the production of nitric acid. N2O is a powerful greenhouse gas that is 300 times more effective at trapping heat than carbon dioxide.
Carbon dioxide (CO2) is a greenhouse gas that is produced by the burning of fossil fuels, such as coal, oil, and natural gas. CO2 is also produced by natural processes such as respiration and the decay of organic matter. CO2 is the most important greenhouse gas because it is the most abundant. CO2 is also a very long-lived gas, which means that it can remain in the atmosphere for hundreds of years.
Methane (CH4) is a greenhouse gas that is produced by natural processes such as the decomposition of organic matter in wetlands and landfills. Methane is also produced by human activities such as the production and transport of natural gas, the cultivation of rice, and the raising of livestock. Methane is a powerful greenhouse gas that is 25 times more effective at trapping heat than carbon dioxide.