Which word is best defined as "full of difficulty or confusion"?

The word "perplexed" is indeed best defined as "full of difficulty or confusion." When someone is perplexed, they find themselves in a state of confusion or puzzlement, often due to a challenging situation or a complex problem that they cannot easily understand. The emotional response associated with being perplexed reflects the struggle to make sense of an issue, which aligns closely with the given definition.

The other options, while having distinct meanings, do not convey the same sense of difficulty or confusion. "Profuse" refers to something that is abundant or excessive, "persnickety" describes a person who is particular or fussy about details, and "precarious" pertains to situations that are uncertain or unstable, which implies risk rather than confusion.