Which instrument of national power pertains to restricting an enemy's financial resources?

The correct choice refers to the financial instrument of national power, which is primarily concerned with the management and strategic use of economic resources to influence the capabilities and actions of a state or organization. This can involve measures such as sanctions, trade restrictions, or strategic investments aimed at limiting an enemy’s access to funds necessary for military operations or other vital functions. By applying financial pressure, a nation can weaken an adversary's ability to sustain its efforts, thus enhancing its own security and achieving its objectives effectively.

The other instruments—military, diplomatic, and informational—play distinct roles in national strategy. The military focuses on the use of armed forces, while diplomatic efforts involve negotiations and alliances to maintain peace or achieve policy goals. Informational instruments aim to influence public perception and opinion. Each of these instruments complements the financial approach, but they do not directly address the economic levers that can restrict an adversary's financial resources.