What is the purpose of the 10th Amendment?

Why this is the answer

The 10th Amendment is the last one in the Bill of Rights, and it draws the line between the federal government and the states. Any power that the Constitution does not give to the federal government, and does not forbid to the states, belongs to the states or to the people. It is the constitutional basis for federalism: the federal government has only the powers written down for it, and everything else stays closer to home. Memory hook: not listed for the federal government means left to the states and the people.