liquid nitrogen vs nitrogen

liquid nitrogen and nitrogen both are nouns.

Word	Noun	Adjective	Verb	Adverb
liquid nitrogen	Yes	No	No	No
nitrogen	Yes	No	No	No

As nouns, nitrogen is a hypernym of liquid nitrogen; that is, nitrogen is a word with a broader meaning than liquid nitrogen:

liquid nitrogen: nitrogen in a liquid state
nitrogen: a common nonmetallic element that is normally a colorless odorless tasteless inert diatomic gas; constitutes 78 percent of the atmosphere by volume; a constituent of all living tissues

Other hypernyms of liquid nitrogen include atomic number 7, N, cryogen.

liquid nitrogen (noun)	nitrogen (noun)
nitrogen in a liquid state	a common nonmetallic element that is normally a colorless odorless tasteless inert diatomic gas; constitutes 78 percent of the atmosphere by volume; a constituent of all living tissues