Compound Odor Boiling Point, °C Flammability

Question

Ammonia Yes -33.3 Yes
Methyl vinyl ether Slight 12.0 Yes
Methyl chloride Yes -33.9 Yes
Sulfur dioxide Yes -10.0 No
Ethynyl bromide Yes 4.7 Yes
Freon 134a No -26.1 No
Carbon dioxide No -28.9 No

Good refrigerants are compounds that evaporate easily and are colorless, odorless, tasteless and chemically inert. Which of those listed below is(are) not suitable as good refrigerant(s)?
Question 1 options:

1) Sulfur dioxide.

2) Methyl chloride.

3) All of the options are not suitable as good refrigerants.

4) Ammonia.

5) Ethynyl bromide.

Answer 1

i think it is sulfur but just go with your gut.

Answer 2

SO2 was used at one time but isn't being used now. Ditto for NH3. Both are good refrigerants but both are lethal if a gas leak occurs in the system.
Freon 134a is being used now.
Here is a link that discusses CO2. It isn't as good as the others but has some benefits. http://refrigerationandairconditioning.danfoss.us/refrigerants/co2/#/
Methyl chloride was used at one time but not now (in consumer refrigeration) due to its toxicity as well as its flammability.
I couldn't find anything on ethynyl bromide but here is a good summary of refrigerant properties.
https://en.wikipedia.org/wiki/Refrigerant