national capital vs Colombo

national capital and Colombo both are nouns.

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

national capital (noun)	Colombo (noun)
the capital city of a nation	the capital and largest city of Sri Lanka; has one of the largest harbors in the world; is located on the western coast of the island of Ceylon