national capital vs Khartoum

national capital and Khartoum both are nouns.

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

national capital (noun)	Khartoum (noun)
the capital city of a nation	the capital of Sudan located at the confluence of the Blue Nile and White Nile