mental capacity vs intelligence

mental capacity and intelligence both are nouns.

Word	Noun	Adjective	Verb	Adverb
mental capacity	Yes	No	No	No
intelligence	Yes	No	No	No

As nouns, intelligence is a hypernym of mental capacity; that is, intelligence is a word with a broader meaning than mental capacity:

mental capacity: mental ability
intelligence: the ability to comprehend; to understand and profit from experience

mental capacity (noun)	intelligence (noun)
mental ability	the operation of gathering information about an enemy
	the ability to comprehend; to understand and profit from experience
	information about recent and important events
	secret information about an enemy (or potential enemy)
	a unit responsible for gathering and interpreting information about an enemy