Phase Change and Lowest Boiling Point

Dorj

I am studying for the MCAT and I am having a hard time understanding the rationale for the following question from my review:

Q: One of the limitations of using a gas as a shock absorbing cushion is that under high pressure, the gas may liquefy and lose compressibility. Which of the following gases would be the best one to use in light of this concern? A. CO2, B. Water vapor, C. Bromine gas, D. Ammonia gas.

The correct answer was A as it had the lowest boiling point and the answer key just states that we want to pick the gas with the lowest boiling point, without explaining why. I am having a hard time understanding why, isn't it more reasonable to go with a gas with a higher boiling point in a high pressure situation, so that more of it remains in the gaseous form.

I am confused. Can someone please explain why lower bp is better in this context.

chemisttree

What if its boiling point were just below room temperature? Wouldn't pressurizing it cause it to immediately condense? How about if its boiling point were even HIGHER that room temperature? Still a good gas for this application?

Borek

To put it differently - imagine filling a shock absorber wit water at room temperature. Would it work?