Answer :
It was "b) the Kansas-Nebraska Act" that led to the end of the Whig Party. The northern and southern Whigs disagreed over the legislation, and the party had been in decline for a decade.
b) Kansas-Nebraska Act
The passage of the Kansas-Nebraska Act pulled together many groups from the North including the Whigs to form the Republican Party.
The Kansas-Nebraska Act allowed for popular sovereignty in Kansas and Nebraska to decide if slavery would be allowed in the states. The change from the Compromise of 1850 angered many groups against the spread of slavery. This pulled together groups such as the Whigs, Free-Soilers, Know-Nothings, and Liberty Party members. These groups formed the Republican Party in hopes of forming a coalition to defeat the expansionist Democratic Party centralized in the South.