"scientific" racism was used to justify negative attitudes toward both slaves and immigrants from (apex)

Scientific racism:

Scientific racism is a pseudo scientific belief based on experiential evidence so as to justify racism, racial superiority or racial inferiority.

Scientific racism became very much common from 1600's to the end of World War II whereas in mid 20th century scientific racism was heavily criticized as discredited.

There were many people who used to support this concept of scientific racism based upon the belief which was in existence and significance of such racial categories. People also believed in the hierarchy of superior and inferior races.

the answer is a. laws were enacted in the aftermath of the plot to make it harder to free slaves,increasing sectionalism