CO2 vs carbonic acid gas

CO2 and carbonic acid gas both are nouns.

Word	Noun	Adjective	Verb	Adverb
CO2	Yes	No	No	No
carbonic acid gas	Yes	No	No	No

As nouns, CO2 and carbonic acid gas are synonyms defined as:

CO2 and carbonic acid gas: a heavy odorless colorless gas formed during respiration and by the decomposition of organic substances; absorbed from the air by plants in photosynthesis

Other synonyms of CO2 include carbon dioxide.

CO2 (noun)	carbonic acid gas (noun)
a heavy odorless colorless gas formed during respiration and by the decomposition of organic substances; absorbed from the air by plants in photosynthesis	a heavy odorless colorless gas formed during respiration and by the decomposition of organic substances; absorbed from the air by plants in photosynthesis