national capital vs Masqat

national capital and Masqat both are nouns.

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

national capital (noun)	Masqat (noun)
the capital city of a nation	a port on the Gulf of Oman and capital of the sultanate of Oman