U.S. Treasury bonds are considered to have the least risk among the options listed due to the full faith and credit of the U.S. government backing them. This makes them virtually default-free, as the government has the authority to raise taxes and print money, ensuring it can meet its debt obligations. As a result, Treasury bonds are seen as a safe investment option, especially during times of economic uncertainty or market volatility.
In contrast, corporate bonds carry higher risk as they are subject to the financial health of the issuing corporation; if the company faces difficulties, it may default on payments. Municipal bonds, while also relatively safe, can have varying levels of risk depending on the financial stability of the issuing municipality. High-yield bonds are the riskiest of the options listed, as they are issued by companies with lower credit ratings, increasing the likelihood of default.