Which one of the following is not a main source of tax revenue for the federal government?

A. Interest on the national debt

B. Taxes on business earnings

C. Taxes on personal income

D. Social security taxes

Interest on the national debt is not a main source of tax revenue for the federal government. The correct option among all the options given in the question is option "A". Taxes on personal income and business income is one of the main source of tax revenue for the federal government. Maximum part of it goes for paying the national debt.