Which of the following is not considered a common refrigerant?

Nitrogen oxide is not considered a common refrigerant, primarily because it does not possess the necessary thermodynamic properties that make a substance effective for refrigeration purposes. Effective refrigerants need to be able to absorb heat at low temperatures and pressures while releasing heat at higher temperatures and pressures.

Carbon dioxide, methyl chloride, and sulfur dioxide, on the other hand, are recognized as refrigerants in various applications. Carbon dioxide is used commonly in modern refrigeration systems due to its low environmental impact and effectiveness as a heat transfer fluid. Methyl chloride has historically been used in refrigeration but is less common today due to toxicity concerns. Sulfur dioxide was used as a refrigerant in the past but has largely been phased out due to safety and environmental considerations.

Nitrogen oxide does not have these properties suitable for refrigeration and is more commonly associated with air pollution and environmental concerns rather than refrigeration technology.