The correct answer is option 4, Nitrogen. Nitrogen is not classified as a greenhouse gas. Greenhouse gases are gases that trap heat in the Earth`s atmosphere, contributing to the greenhouse effect and global warming. While water vapor, chlorofluorocarbons (CFCs), and methane are all greenhouse gases, nitrogen does not possess the same properties.

Option 1, water vapor, is a significant greenhouse gas. It is produced through evaporation and is a natural part of the Earth`s water cycle. Water vapor acts as a strong reflector of infrared radiation, trapping heat in the atmosphere.

Option 2, chlorofluorocarbons (CFCs), are synthetic compounds commonly used in refrigeration and aerosol propellants. CFCs have destructive effects on the ozone layer and are potent greenhouse gases.

Option 3, methane, is a potent greenhouse gas that is produced through natural processes like decomposition and the digestive systems of animals. Methane has a much higher warming potential than carbon dioxide.

Therefore, while options 1, 2, and 3 are greenhouse gases, option 4, Nitrogen, is not a greenhouse gas.