Which of the following is an important Green house Gas?  A. Carbon Dioxide  B. Chlorofluorocarbon  C. Carbon Monoxide  D. Freon

The answer is A. Carbon Dioxide. Here's why:

1. Greenhouse gases are gases in Earth's atmosphere that trap heat. They let sunlight pass through the atmosphere, but they prevent the heat that the sunlight brings from leaving the atmosphere. The main greenhouse gases are: Water vapor, Carbon dioxide, Methane, Nitrous oxide, and Ozone.

2. Carbon Dioxide (CO2): This is the most important greenhouse gas released by human activities, specifically, the burning of fossil fuels (coal, oil, and natural gas) for energy and transportation. It is also released during the process of deforestation.

3. Chlorofluorocarbon (CFC): While CFCs are indeed greenhouse gases, they are not naturally occurring and are instead man-made. They were widely used in the 20th century as refrigerants, aerosol propellants, and in air conditioners. However, their production has been phased out due to their role in ozone depletion, not specifically for their contribution to global warming.

4. Carbon Monoxide (CO): This is not a significant greenhouse gas, as it does not effectively trap heat in the atmosphere. While it is produced by human activities, such as the burning of fossil fuels, its contribution to global warming is minimal.

5. Freon: This is a brand name for a type of CFC, so the same information applies. It is a greenhouse gas, but not naturally occurring, and its production has been phased out due to its role in ozone depletion.

So, out of the options given, Carbon Dioxide is the most important greenhouse gas.