national capital vs Christiania

national capital and Christiania both are nouns.

Word	Noun	Adjective	Verb	Adverb
national capital	Yes	No	No	No
Christiania	Yes	No	No	No

national capital (noun)	Christiania (noun)
the capital city of a nation	the capital and largest city of Norway; the country's main port; located at the head of a fjord on Norway's southern coast