Ar vs atomic number 18

Ar and atomic number 18 both are nouns.

Word	Noun	Adjective	Verb	Adverb
Ar	Yes	No	No	No
atomic number 18	Yes	No	No	No

As nouns, Ar and atomic number 18 are synonyms defined as:

Ar and atomic number 18: a colorless and odorless inert gas; one of the six inert gases; comprises approximately 1% of the earth's atmosphere

Other synonyms of Ar include argon.

Ar (noun)	atomic number 18 (noun)
a colorless and odorless inert gas; one of the six inert gases; comprises approximately 1% of the earth's atmosphere	a colorless and odorless inert gas; one of the six inert gases; comprises approximately 1% of the earth's atmosphere