Question

Which of the following is used as refrigerant?
[This question has multiple correct options.]
A. Solid $C{O_2}$
B. $CHC{l_3}$
C. $SiC$
D. $C{F_2}C{l_2}$

Answer 1

A refrigerant is a substance or mixture, usually a fluid, used in a heat pump and refrigeration cycle. In most cycles it undergoes phase transitions from a liquid to a gas and back again. Many working fluids have been used for such purposes. Fluorocarbons, especially chlorofluorocarbons, became commonplace in the 20th century, but they are being phased out because of their ozone depletion effects.

Complete answer:
A refrigerant would have favorable thermodynamic properties, be non corrosive to mechanical components, and be safe, including freedom from toxicity and flammability. It would not cause ozone depletion or climate change. The common chemical compounds that show a promising effect as a refrigerant are solid $C{O_2}$, ammonia, chlorofluorocarbons, etc. Although the chlorofluorocarbons affect the ozone layer by tearing apart the ozone present in the upper troposphere, it still is used as a common refrigerant. The $C{F_2}C{l_2}$is one of the major refrigerants used in the 20th and 21st century.

Thus, the correct options are: A. Solid $C{O_2}$ and D. $C{F_2}C{l_2}$.

Note:
Since different fluids have the desired traits in different degrees, choice is a matter of trade-offs. The desired thermodynamic properties are a boiling point somewhat below the target temperature, a high heat of vaporization, a moderate density in liquid form, a relatively high density in gaseous form, and a high critical temperature. Since boiling point and gas density are affected by pressure, refrigerants may be made more suitable for a particular application by appropriate choice of operating pressures.