perplexity vs mental confusion

perplexity and mental confusion both are nouns.

Word	Noun	Adjective	Verb	Adverb
perplexity	Yes	No	No	No
mental confusion	Yes	No	No	No

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

perplexity: trouble or confusion resulting from complexity
mental confusion: a mental state characterized by a lack of clear and orderly thought and behavior

Other hypernyms of perplexity include confusedness, confusion, disarray, muddiness.

perplexity (noun)	mental confusion (noun)
trouble or confusion resulting from complexity	a mental state characterized by a lack of clear and orderly thought and behavior