national capital vs San Marino

national capital and San Marino both are nouns.

Word	Noun	Adjective	Verb	Adverb
national capital	Yes	No	No	No
San Marino	Yes	No	No	No

national capital (noun)	San Marino (noun)
the capital city of a nation	the smallest republic in the world; the oldest independent country in Europe (achieved independence in 301); located in the Apennines and completely surrounded by Italy
	the capital and only city of San Marino