Final answer:
The duty of the Legislative branch is to make laws, and one duty they do not have is to approve treaties.
Step-by-step explanation:
The duty of the Legislative branch is to make laws. Therefore, the option that is NOT a duty of the Legislative branch is Approve treaties. The approval of treaties is a duty of the Executive branch, specifically the President, who has the power to negotiate and sign treaties with foreign countries.
Learn more about Legislative branch and their duties