Refrigerants in household refrigerators (legacy context) Which refrigerant has been widely used historically in domestic refrigerators?

Introduction / Context:
Domestic refrigerators have used several refrigerants over the last century. Understanding which fluids were common in home appliances helps students link thermodynamic properties (pressure levels, toxicity, flammability) to system design and safety standards.

Given Data / Assumptions:

• Question asks about the refrigerant widely used in household refrigerators in traditional/legacy contexts.
• Focus is on common mass-market units rather than special laboratory or industrial systems.
• Environmental phase-outs (e.g., of CFCs) do not change what was historically most prevalent.

Concept / Approach:
R-12 (a CFC) was historically the dominant choice in domestic refrigerators for many decades because it is noncorrosive, nonflammable, and compatible with mineral oils, with moderate pressures that suit small hermetic compressors. Although R-12 has now been phased out due to ozone depletion concerns and replaced largely by R-134a or newer low-GWP blends, the historical answer remains R-12.

Step-by-Step Solution:
Identify legacy domestic practice: small hermetic compressors + safe, stable refrigerant.Match properties: R-12 offered low toxicity, low discharge temperature, and good oil miscibility.Therefore, the historically widespread domestic refrigerant is R-12.

Verification / Alternative check:
Manufacturer literature and refrigeration handbooks list R-12 for domestic units before environmental regulations led to R-134a transitions.

Why Other Options Are Wrong:
Ammonia is efficient but toxic and corrosive to copper; rarely used in home fridges. CO2 uses very high pressures and is uncommon in legacy domestic units. SO2 was used early on but was replaced due to toxicity. R-22 is mainly for air-conditioning, not typical household refrigerators.

Common Pitfalls:
Confusing modern replacements (like R-134a) with the historically “widely used” fluid specified by older curricula.

Final Answer:
R-12 (dichlorodifluoromethane)