Final answer:
The necessary and proper clause justifies the "implied powers doctrine" in the Constitution.
Step-by-step explanation:
The clause in the Constitution that justifies the "implied powers doctrine" is the necessary and proper clause. This clause, also known as the elastic clause, is found in Article I, Section 8, Clause 18 of the Constitution. It grants Congress the power to make all laws which shall be necessary and proper for carrying out its enumerated powers.
Learn more about Implied powers doctrine in the Constitution