The correct answer is: A. Carbon dioxide (CO2)
Carbon dioxide is the most abundant greenhouse gas in the Earth’s atmosphere. It is a naturally occurring gas that is released into the atmosphere when fossil fuels are burned, such as coal, oil, and natural gas. Carbon dioxide is also released when trees are cut down and when soil is disturbed.
Carbon dioxide is a greenhouse gas because it traps heat in the atmosphere. This heat helps to keep the Earth warm, but it also contributes to climate change.
The other options are also greenhouse gases, but they are not as abundant as carbon dioxide. Nitrous oxide is the second most abundant greenhouse gas, followed by methane and water vapor. Chlorofluorocarbons (CFCs) are synthetic greenhouse gases that were once widely used in refrigerants and aerosol propellants. However, they have been banned since the 1980s because they damage the ozone layer.
Here is a brief explanation of each option:
- Carbon dioxide (CO2): Carbon dioxide is a colorless, odorless gas that is produced when fossil fuels are burned. It is also released when trees are cut down and when soil is disturbed. Carbon dioxide is the most abundant greenhouse gas in the Earth’s atmosphere.
- Nitrous oxide (N2O): Nitrous oxide is a colorless, odorless gas that is produced by the decay of organic matter. It is also released by the use of fertilizers and by some industrial processes. Nitrous oxide is the second most abundant greenhouse gas in the Earth’s atmosphere.
- Methane (CH4): Methane is a colorless, odorless gas that is produced by the decomposition of organic matter. It is also released by the digestive system of ruminant animals, such as cows and sheep. Methane is the third most abundant greenhouse gas in the Earth’s atmosphere.
- Water vapor (H2O): Water vapor is a colorless, odorless gas that is produced when water evaporates. It is also released by plants during transpiration. Water vapor is the most abundant greenhouse gas in the Earth’s atmosphere, but it is not as potent a greenhouse gas as carbon dioxide, nitrous oxide, or methane.
- Chlorofluorocarbons (CFCs): Chlorofluorocarbons (CFCs) are synthetic chemicals that were once widely used in refrigerants and aerosol propellants. However, they have been banned since the 1980s because they damage the ozone layer. CFCs are very potent greenhouse gases.