Which of the following is not a power of the united states congress?
a. establishing and paying for the armed forces
b. enforcing immigration laws
c. regulating commerce between the states
d. levying and collecting taxes

The federal government of the USA (the United States Congress) consists of two chambers: the Senate and the House of Representatives. 
The Congress has authority over financial and budgetary matters and it is responsible for the common defense and general welfare of the United States.
Enforcing immigration laws is not a power of the United States Congress.
(Solution:B)

The correct answer is
B. Enforcing immigration laws

Enforcing laws is a part of the executive branch and not of the congress which is the legislative branch. They can make laws but their enforcing goes down to the federal police or local state police departments or sheriffs and such people. The judicial branch decides whether such laws are constitutional.