Among common historical refrigerants (e.g., ammonia, carbon dioxide, sulphur dioxide, R-12), does sulphur dioxide (SO₂) have the lowest normal boiling point?

Introduction / Context:
Boiling point at standard pressure is a key selection factor for refrigerants. Lower normal boiling point generally indicates stronger cooling potential at low evaporator temperatures, though toxicity, flammability, and environmental impact also matter.

Given Data / Assumptions:

• Comparison uses approximate normal boiling points at 1 atm.
• Typical references: NH₃ (ammonia), CO₂, SO₂, and R-12.

Concept / Approach:
SO₂ has a normal boiling point near −10 °C, whereas ammonia is about −33 °C and R-12 about −30 °C. Carbon dioxide does not have a normal liquid boiling point at 1 atm (it sublimates at about −78.5 °C), and its critical temperature is near 31 °C; thus, at 1 atm it exists as either gas or dry ice, not a liquid. Therefore, SO₂ is not the lowest among these; in fact, it is comparatively high (warmer) among traditional refrigerants.

Step-by-Step Solution:

Verification / Alternative check:
Data tables corroborate NH₃ and R-12 having lower boiling points than SO₂ at standard pressure; CO₂ does not boil at 1 atm, indicating even stronger low-temperature behavior via sublimation reference.

Why Other Options Are Wrong:

• (a) Incorrect: SO₂ is not the lowest.
• (c) Boiling points differ widely.
• (d) While boiling point depends on pressure, standard comparisons use 1 atm.
• (e) Altitude changes pressure but does not invert the ordering cited.

Common Pitfalls:
Confusing SO₂’s historical use with superior low-temperature properties; toxicity and corrosion issues limited its application.

Final Answer:
No, SO₂ does not have the lowest boiling point