In which section of the Constitution is Congress' power limited?

The correct answer is found in Article I Section 9 of the Constitution, which explicitly outlines the limitations placed on Congress and restricts certain actions. This section includes a list of prohibitions, such as the inability to pass ex post facto laws, bill of attainder laws, and any law that would grant titles of nobility. By detailing these limitations, this portion of the Constitution aims to protect individual rights and maintain a system of checks and balances within the federal government.

The other sections mentioned in the question focus on different aspects of government structure and powers. Article I Section 10 is focused on prohibitions on the states rather than Congress, while Article II Section 2 pertains to the President's powers, including the power to make treaties and appoint officials. Article III Section 1 establishes the judicial branch and does not limit Congressional powers. This distinction highlights how Article I Section 9 specifically addresses the constraints on Congress, making it the correct answer in this context.