Greenhouses gases causing a rise of 3℃ rise in the overall global temperature in the past century are CFCs. The CFC used in refrigerators is

The correct option is Freon.

Chlorofluorocarbons (CFCs) are a group of synthetic organic compounds containing carbon, chlorine, and fluorine atoms. Because of their chemical stability, low toxicity, non-flammability, and ease of liquefaction, they were historically widely adopted in industrial and domestic applications.

Freon is a registered trademark of DuPont used for a variety of halocarbon products. The most common CFC used as a refrigerant in domestic refrigerators and air conditioners was Freon-12 (dichlorodifluoromethane, chemical formula CF₂Cl₂). Due to its thermodynamic properties, it served as an excellent heat transfer fluid in cooling cycles.

Let us look at why the other options are not the correct choice:
• Ammonia: Although ammonia (NH₃) is used as a refrigerant in large-scale industrial systems, it is an inorganic compound and not a CFC.
• Methane: Methane (CH₄) is a hydrocarbon and a greenhouse gas, but it is not a CFC and is not used as a standard refrigerant in household refrigerators.
• Carbon dioxide: Carbon dioxide (CO₂) is a major greenhouse gas, but it is not a CFC.