List at least THREE reasons some of the African American representatives were determined to be unable to serve​

Hello. Your question is incomplete, which makes it difficult for it to be answered correctly. However, I will try to help you in the best possible way.

If you are referring to African-Americans who were considered unable to serve at the national congress. This happened due to prejudice, the belief that blacks did not have full political knowledge and the attempt by white politicians not to allow the black population to have political representation, as a way to keep the white population superior and dominant.

congress also has implied powers, which derive from the necessary and proper clause of the constitution and permit congress "to make all laws which shall be necessary and proper for carrying into execution the foregoing powers, and all other powers vested by this constitution in the government of the united states.