The statement that BEST explains why the decision made in the "Dred Scott" case nullified the Compromise of 1850 and "popular sovereignty" is:
B) Slaves were considered property and the federal government could not disallow slavery in any state.
The Dred Scott decision asserted that enslaved individuals were considered property, which meant that the federal government could not prohibit slavery in any territory or state. This directly undermined the principles of the Compromise of 1850 and the framework of popular sovereignty, which allowed the territories to determine their own status regarding slavery.