The outcome of the Supreme Court's Dred Scott case decided that

A. Slaves that lived on free soil after one year were free.

B. slaves could sue for freedom in a federal court.

C. Slaves were not citizens, but the property of their owner.

D. slaves could purchase freedom after gaining citizenship.

C. Slaves were not citizens, but the property of their owner.

Option C, is the correct answer.

Explanation:

On 6th March 1857, the supreme court of the U. S. in a case (Dred Scott v. Sandford) announced that a slave who is residing in the free state and region of the U. S. was not permitted to his freedom and that the African - Americans were not and could nevermore be subject of the citizenship of the U. S. Moreover, the Supreme Court declared that Congress does not possess any power to exclude slavery from various states of the U. S.