1. Fluorine is a nonmetallic chemical element with chemical symbol F and atomic number 9. Fluorine is one of the halogen elements, belonging to the group ⅶ A of the periodic system, which is located in the second period of the periodic table. The elemental fluorine is F2, which is a light yellow and highly toxic gas. Fluorine gas is highly corrosive and extremely active in chemistry. It is one of the most oxidizing substances and can even react with some inert gases under certain conditions.

2. Freon, whose name comes from English Freon, is a trademark of refrigerant registered by DuPont Company in the United States. In China, there are differences in the definition of freon, which is generally defined as the general name of halogenated compounds of saturated hydrocarbons (mainly methane, ethane and propane). According to this definition, freon can be divided into four categories: CFC, HCFC and HFC. Some scholars define freon as CFC refrigerant; Freon only refers to dichlorodifluoromethane (CCl? F? R12, a kind of CFC).

Freon is colorless gas or volatile liquid at room temperature, tasteless or slightly odorous, non-toxic or low-toxic, and its chemical properties are stable.

CFC refrigerants, such as dichlorodifluoromethane, have been restricted in use because they destroy the atmospheric ozone layer. There have been many holes in the ozone layer on the earth, and some holes have exceeded the area of Africa, which is largely due to the chemical properties of CFCs. Another harm of freon is the greenhouse effect.