Kr vs noble gas

Kr and noble gas both are nouns.

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

As nouns, noble gas is a hypernym of Kr; that is, noble 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
noble gas: any of the chemically inert gaseous elements of the helium group in the periodic table

Other hypernyms of Kr include argonon, inert gas.

Kr (noun)	noble 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