There is no gas that *does not* liquefy under the right conditions.

Here's why:

* All gases can be liquefied: Every gas has a critical temperature and pressure. Above the critical temperature, no amount of pressure can force the gas into a liquid state. However, below the critical temperature, increasing pressure will eventually cause the gas to condense into a liquid.

* Extreme conditions: Even gases like helium, which has a very low critical temperature of -268.93°C (-452.07°F), can be liquefied under high pressure.

So, while some gases may be more difficult to liquefy due to their extremely low critical temperatures, it's inaccurate to say any gas will never liquefy.