I'm going with B! I would say it is the right answer
The Kansas-Nebrask Act was an 1854 bill that mandated “popular sovereignty”–allowing settlers of a territory to decide whether slavery would be allowed within a new state's borders. ... Kansas was admitted as a free state in January 1861 only weeks after eight Southern states seceded from the union.Oct 29, 2009
Answer: They opposed it because they suspected that new states formed in the Louisiana Territory would be Republican and thus jeopardize the balance of power. Some Federalists planned to secede from the Union.