Gold is not a marketable security.
In the case of liquidation, common stockholders are the last in the list of recipients of the cash of the company. Therefore, it has more risk than securities whose holders have a higher priority in the case of liquidation.
Of the choices provided, the commercial paper of a Aaa-rated company is the marketable security that has the lowest risk. It has less risk than common stock because the holders of debt have a preference over holders of common stock in the distribution of assets in case of liquidation of the company. It has less risk than municipal bonds, even municipal bonds that may be Aaa rated, because commercial paper is very short-term debt. There is much less chance of something happening to change the financial condition of the issuer and the rating of a short-term debt instrument than there is of something happening to change the financial condition of the issuer and the rating of a long-term debt instrument like a municipal bond, simply because there is less time for something like that to happen. Therefore, Aaa rated commercial paper carries less risk than municipal bonds.
Bonds are longer-term debt, and longer-term debt carries more risk than short-term debt because there is more time for something to happen that could change the financial condition of the issuer and its ability to repay the debt.
