Yes, most of refrigeration gases are heavier than air. This is because they are made up of molecules that are larger and heavier than the molecules of air.  All of these refrigerant gases are denser than air.

No, the freezing point of the refrigerant should be well below the expected evaporator temperature.

The freezing point of the refrigerant is the temperature at which the refrigerant will change from a liquid to a solid. The freezing point of the refrigerant should be well below the expected evaporator temperature. If the refrigerant freezes in the evaporator, it will not be able to absorb heat and the evaporator will not be able to cool.

Yes, refrigerant shall have higher critical pressure and higher critical temperature. The critical point of a refrigerant is the point at which the refrigerant can no longer be liquefied by increasing pressure. The critical pressure and temperature of a refrigerant are important because they determine the range of temperatures and pressures at which the refrigerant can be used. Higher critical pressure and temperature refrigerants can be used in a wider range of applications ( Ex: used in hotter climates)

R22, also known as HCFC-22, is a hydrochlorofluorocarbon (HCFC) that is used as a refrigerant in air conditioners and refrigerators. R-410a is a good replacement for R-22 refrigerant. It is a hydrofluorocarbon (HFC) that is non-ozone depleting and has a lower global warming potential than R-22. R-410a is also more energy efficient than R-22. R 410a properties are similar to R-22, therefore  is also compatible with existing equipment operating on R-22

As per ASHRAE, refrigerant class 3 has high flammability. Some of the examples are:

CO2 refrigerant has high operating pressure. This means that CO2 systems require stronger and more expensive components than systems that use other refrigerants. This is one the main disadvantages of CO2 refrigerant

Dielectric strength is the ability of a material to withstand an electric field without breaking down refrigerant and allowing current to flow. It is the electrical insulation property of the refrigerant. It is desirable for refrigerants to have high dielectric strength in order to prevent arcing and sparking, which can lead to fires.

Hydrofluorocarbons (HFCs) refrigerants are not ozone-depleting substances. HFCs are known to have a high global warming potential (GWP), which is a measure of their ability to trap heat in the atmosphere over a specific time period compared to carbon dioxide (CO2). The most commonly used HFC-410A has GWP of 2,088

If the freezing point of a refrigerant is too high, it will not be able to absorb heat effectively in the evaporator. This can lead to poor refrigeration performance. Therefore refrigerants are desired to have low freezing point.

An azeotropic refrigeration blend is a mixture of two or more refrigerants that has a constant boiling point over a wide range of pressures. Azeotropic blends are often used in refrigeration systems because they are more efficient than pure refrigerants. This is because the mixture has a lower boiling point than the pure refrigerants, which allows the system to operate at a lower pressure. Azeotropic blends are also more stable than pure refrigerants.

The Ozone Depletion Potential (ODP) of R-11, also known as CFC-11, is 1.0. The ODP is a measure of the potential of a substance to deplete the ozone layer, with CFC-11 having the highest ODP value of 1.0

CFCs are chemically inert and do not react with other chemicals in the lower atmosphere.

Ammonia is highly toxic and highly flammable.  However, Ammonia is used as a refrigerant because it is a very effective heat pump. It has a high boiling point, which means that it can absorb a lot of heat before it vaporizes. Ammonia is also relatively inexpensive and easy to obtain.

R401a is an azeotropic blend of R125 and R134a, while R407C is a zeotropic blend of R32, R125, and R134a. Azeotropic blends have a constant boiling point over a wide range of pressures, while zeotropic blends have a variable boiling point. This means that R401a will vaporize and condense at the same temperature, regardless of the pressure. Therefore R401a more efficient at cooling than R407C