Freezing point comparison Relative to common halocarbon refrigerants, R-12 (dichlorodifluoromethane) has which characteristic for freezing point?

Introduction / Context:
Refrigerant selection considers numerous properties: boiling point, critical temperature, miscibility with oil, toxicity, and freezing point. A very low freezing point helps avoid solidification in low-temperature applications and ensures reliable flow through capillaries and valves.

Given Data / Assumptions:

• Comparison among typical pure refrigerants; R-12 historically used in domestic systems (legacy context).
• Freezing point is a substance property at atmospheric pressure and does not depend on condenser pressure.

Concept / Approach:
R-12 has an extremely low freezing point (around −157°C), lower than most common halocarbons traditionally used for comfort cooling and domestic refrigeration. Thus, within that family it is regarded as having a very low (i.e., “lowest”) freezing point, a favorable attribute for flow assurance.

Step-by-Step Solution:
Recognize the property: freezing point is intrinsic and notably low for R-12.Compare to other common refrigerants of similar era; R-12's freezing point is among the lowest.Therefore select “Lowest.”

Verification / Alternative check:
Property tables show R-12 with a much lower freezing point than, for example, R-22 or R-134a, confirming suitability for low-temperature lines without risk of solidification.

Why Other Options Are Wrong:
“Highest” contradicts data; “equal to ammonia” is incorrect because ammonia has different crystalline behavior; dependence on condenser pressure is irrelevant to the freezing point of a pure substance.

Common Pitfalls:
Confusing freezing point with boiling point or with the temperature glide of blends.

Final Answer:
Lowest