The Federal Budget is the instrument by which the government implements:

Fiscal policy, is the right answer.

Explanation:

The Federal Budget is a written document through which the government of the United States estimates the revenue and spending for every fiscal year. Through this document, the government of the United States can expect the amount of money that is to be received for a particular year and approve the amount that the government can spend. In this way, the federal budget is an instrument to implement the fiscal policy.

The government implements fiscal policy in order to achieve economic growth, price stability and full employment. Such decisions are taken during the creation of the federal budget.