The Supreme Court's ruling in the Scott v. Sandford case declared which of the following was unconstitutional?

The Supreme Court's ruling in the Scott v. Sandford case declared that African Americans, no matter what their status were not American citizens. This therefore made it unconstitutional for them to sue in federal court and that the federal government did not have the power to regulate slavery in federal territories following the creation of the United States. This was a landmark decision, as it is the second time in all of the United States history that the Supreme Court decided that an Act of Congress was unconstitutional.