protactinium vs atomic number 91

protactinium and atomic number 91 both are nouns.

Word	Noun	Adjective	Verb	Adverb
protactinium	Yes	No	No	No
atomic number 91	Yes	No	No	No

As nouns, protactinium and atomic number 91 are synonyms defined as:

protactinium and atomic number 91: a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead

Other synonyms of protactinium include Pa, protoactinium.

protactinium (noun)	atomic number 91 (noun)
a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead	a short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead