Mekong vs mainland China

Mekong and mainland China both are nouns.

Word	Noun	Adjective	Verb	Adverb
Mekong	Yes	No	No	No
mainland China	Yes	No	No	No

Mekong (noun)	mainland China (noun)
an Asian river; flows through a large delta in southern Vietnam into the South China Sea	a communist nation that covers a vast territory in eastern Asia; the most populous country in the world