What law was found to be unconstitutional in the dred scott decision?

The law that was found to be unconstitutional in the Dred Scott case was the Missouri Compromise.

Explanation:

Dred Scott v. Sandford was a court case, crucial in the history of the United States, resolved by the Supreme Court in 1857, in which it was decided to deprive to all inhabitants of African descent, whether they were slaves or not, the right to citizenship and the authority to ban slavery in federal territories of the country was removed from Congress.

In it, the provisions of the Missouri Compromise were annulled as a legislative act, since it exceeded the powers of Congress, as it attempted to exclude slavery and impart liberty and citizenship to non-white citizens in the north part of the Louisiana Purchase.