8. which is not a duty of a member of congress?

Declaring a law which is unconstitutional is not a duty of a member of congress. The duties of a member of congress are as follows;

Law maker- It is the first and major responsibility of a member of congress to pass a law that is favorable for all the citizens. The citizens must obey it.  

Constituent services and education public- A member of a congress provide assistance and guidance to the constituents or local firm. Then they come up as a teacher or representative.  

Representing people - The Congress represents the people of the United States. The role of a representative is to represent the people and their problems to the government.