Final answer:
The correct limit that the Articles of Confederation placed on Congress was that it could not tax the states to raise funds. This restriction created financial difficulties for the new government.
Step-by-step explanation:
The Articles of Confederation placed several limits on Congress, but of the choices given, the correct answer is option 'a)' Congress could not tax the states to raise funds. While Congress did have the powers to declare war and make treaties, it lacked the essential power to impose taxes on states or individuals. Instead, the national government had to rely on voluntary contributions from the states, which often did not supply the requested funds. Consequently, this created significant challenges for the new nation in paying debts and funding governmental operations.