A
He did indeed marry a free woman, but that was not the basis of his case. In fact both of them sued for their freedom but the lawyers handling the case decided to go with Dred Scott alone and whatever decision was reached about him would apply to her.
B
The physical abuse in states that accepted slavery, was legal.
C
He made that claim. The lower courts rejected it. But the supreme court agreed to hear the case. When you look Dred Scott up, you find out that legal scholars consider it the worst case write up in the history of the Supreme court. Search out comments on Tanney who wrote the opinion of the majority of those voting against Dred Scott. (It was a 7 - 2 vote).
D
It wasn't unconstitutional. That was problem with the constitution for a very long time. The founding fathers did not know what to do about slavery and the Carolinas threatened to succeed if a slavery clause was included in the constitution. They just could not resolve the issue. It had to wait nearly 75 years before it was and then it took a war.
Answer C