Which is the most commonly used refrigerant Freon-12?

The correct answer is (2) Dichlorodifluoromethane.
Freon-12, also known as dichlorodifluoromethane \(\left(\mathrm{CCl}_2 \mathrm{~F}_2\right)\), is a commonly used refrigerant. It was widely used in refrigeration and air conditioning systems for many years until its use was phased out due to concerns about ozone layer depletion.
Here's a quick explanation of the other options:
- (A) Monochloromonofluoromethane: This is Freon-22 (chlorodifluoromethane), another refrigerant but different from Freon-12.
- (C) Chlorodifluoromethane: This is Freon-22, not Freon-12.
- (D) Dichlorofluoromethane: This is not a standard refrigerant name and doesn't correspond to Freon-12.