The gas that is most convenient to use in gas thermometers, as it is almost permanent gas

The gas that is most convenient to use in gas thermometers is helium. Helium is an inert gas that is almost chemically inactive, which makes it a good choice for use in gas thermometers because it does not react with other substances and remains stable over time. This property of helium makes it almost a permanent gas, which means that it can be used repeatedly without the need for frequent replacement. Additionally, helium has a very low boiling point, which makes it useful in low-temperature applications, such as cryogenics. Overall, helium is a popular choice for gas thermometers due to its stability, inertness, and low boiling point.