Answer:
"A counterclaim is an opposing idea or opinion."
Explanation:
The first two such as "A counterclaim is a document or reference that provides information." and "A counterclaim is an opinion or stated idea that not everyone believes." are incorrect and wrong and do not best describe a counterclaim because one is not even what it is and the second is not a counterclaim nor an opinion it is a claim. Therefore 1. and 3. are no gos. The last one is wrong too because its not an argument against an idea its a claim/opinion. Therefore your answer is 2.
Hopefully this helps.
