Ar vs inert gas

Ar and inert gas both are nouns.

Word	Noun	Adjective	Verb	Adverb
Ar	Yes	No	No	No
inert gas	Yes	No	No	No

As nouns, inert gas is a hypernym of Ar; that is, inert gas is a word with a broader meaning than Ar:

Ar: a colorless and odorless inert gas; one of the six inert gases; comprises approximately 1% of the earth's atmosphere
inert gas: any of the chemically inert gaseous elements of the helium group in the periodic table

Other hypernyms of Ar include argonon, noble gas.

Ar (noun)	inert gas (noun)
a colorless and odorless inert gas; one of the six inert gases; comprises approximately 1% of the earth's atmosphere	any of the chemically inert gaseous elements of the helium group in the periodic table