Which type of savings bond is a non-marketable, interest-bearing bond issued at par and purchased only by trading in Series EE bonds at maturity?

The correct answer is Series HH bonds. These bonds are specifically designed as non-marketable, interest-bearing bonds issued by the U.S. Department of the Treasury. Series HH bonds can only be purchased by trading in Series EE bonds when they mature, allowing investors to exchange their mature EE bonds for HH bonds at par value (the face value of the bond).

The distinguishing feature of Series HH bonds is that they do not increase in value like some other savings bonds; instead, they pay interest over time. This makes them a stable option for those looking for a steady income stream rather than an appreciation in value.

In contrast, I-bonds are designed to provide protection against inflation and accrue interest differently, while municipal bonds and general obligation bonds are primarily used by state and local governments to raise funds and can be bought and sold in public markets. They do not fit the specific criteria of being non-marketable or solely being available through the exchange of Series EE bonds at maturity.