Why was the term inert gas once used to refer to noble gases and why is it no longer in common use?

Because unlike inert gas Noble gas sometimes indergo reaction

Explanation:

Inert gas as the name suggest means it can not undergoing reaction at most conditions.But as a science progresses it was found that some group 8 elements under special conditions of temperature and pressure can under go reaction this discovery led to why inert gas is not commonly used

Explanation:

Noble gases are gases that belongs to group 18(8A) in the periodic table, they have 8 electrons in their outermost shell. Examples includes helium, neon, argon, krypton and Radon.

These gases were formerly referred to as inert gases meaning they are chemically inactive, this is because they have a complete octet structure which makes them stable, but as time goes on scientist realised that referring to these gases as inert might not be outrightly correct because :

1.Some members of the noble gases form compounds meaning that they are not inert under all conditions, for example Xenon tetrafluoride

2.Radon is a dangerous radioactive element, it unstable to such an extent that its radioactivity makes any chemical reaction with it almost impossible.

3.Gases like Nitrogen are inert under various conditions.

the reason is because the moon has some form of gravity, and that gravity pulls the ocean tides.