What legislation allowed residents of the Mexican cession to decide the slavery issue for themselves?

The Compromise of 1850 is the correct answer as it included provisions that allowed residents of the newly acquired territories from the Mexican cession to determine whether they would permit slavery within their borders through popular sovereignty. This legislation was a package of five laws aimed at resolving the tensions between slave and free states following the Mexican-American War. By allowing the residents of territories such as California and New Mexico to vote on the issue of slavery, the Compromise sought to balance interests between the North and the South, reflecting a significant shift towards letting states and territories make their own decisions regarding slavery.

In contrast, the other choices do not pertain directly to the residents of the Mexican cession making that determination. The Fugitive Slave Law of 1850 primarily dealt with the capture and return of runaway slaves and enforced penalties for individuals who aided them. The Kansas-Nebraska Act of 1854, while related in that it also permitted popular sovereignty regarding slavery, was focused specifically on the territories of Kansas and Nebraska rather than those gained from the Mexican cession. Dred Scott vs. Sandford was a Supreme Court case that ruled on the status of enslaved people but came after the Compromise and did not give residents the power to decide on slavery directly