Which of the following financial instruments is a type of tax-exempt mutual fund?

Tax-exempt mutual funds are specifically designed to invest in municipal securities, which typically provide interest that is exempt from federal income tax and, in some cases, state and local taxes as well. Among the choices provided, tax-exempt bonds are the correct answer because they represent the underlying securities that these mutual funds invest in.

Investing in tax-exempt bonds allows the fund to distribute tax-free income to its investors, making it an attractive option for individuals in higher tax brackets seeking to minimize their tax liabilities. In contrast, common stocks, certificates of deposit, and exchange-traded funds do not inherently provide tax exemptions related to the income they generate. Thus, tax-exempt bonds are fundamental in characterizing a tax-exempt mutual fund, as they form the crux of the investment strategy aimed at providing tax-free returns to investors.