Final answer:
The duty of the north if slaves escaped and then were caught was to return the slaves back to the south.
Step-by-step explanation:
The duty of the north if slaves escaped and then were caught was B. They had to return the slaves back to the south. This was because of the Fugitive Slave Act of 1850, which required all citizens, including those in the north, to assist in the capture and return of escaped slaves. Failure to comply with this law was considered a crime.
Learn more about Fugitive Slave Act of 1850