Final answer:
The power of the Federal Government to make grants-in-aid is derived from Congress's expressed power to tax and spend for the general welfare as outlined in Article I, Section 8 of the U.S. Constitution, and supported by the 16th Amendment.
Step-by-step explanation:
The power of the Federal Government to make grants-in-aid is linked to the expressed power of Congress to tax and spend for the general welfare of the United States. Specifically, the Constitution enumerates these powers in Article I, Section 8, which provides Congress with the authority to levy taxes, duties, imposts, and excises, to pay the debts and provide for the common defense and general welfare of the United States. This is further supported by the 16th Amendment, which gave Congress the power to establish a federal income tax, creating revenue that could be allocated to states and localities through grants.