An unsecured corporate bond is known as a ____.

An unsecured corporate bond is referred to as a debenture. This type of bond relies solely on the creditworthiness and reputation of the issuing corporation, rather than any specific asset collateralizing the bond. Debentures typically offer higher yields compared to secured bonds because of the increased risk associated with the lack of collateral. Investors are attracted to debentures as they represent a form of debt financing for corporations without tying the obligation to specific assets.

The other options do not apply here: a note generally refers to a type of debt security with a shorter maturity period, a mortgage bond is secured by specific assets of the corporation such as real estate or equipment, and a certificate of deposit is a savings product offered by banks that pays interest over a specified term. Thus, in the context of unsecured corporate bonds, debenture is indeed the correct and most appropriate term.