Kr vs inert gas

Kr and inert gas both are nouns.

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

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

Kr: a colorless element that is one of the six inert gasses; occurs in trace amounts in air
inert gas: any of the chemically inert gaseous elements of the helium group in the periodic table

Other hypernyms of Kr include argonon, noble gas.

Kr (noun)	inert gas (noun)
a colorless element that is one of the six inert gasses; occurs in trace amounts in air	any of the chemically inert gaseous elements of the helium group in the periodic table