Which type of bond gives investors the right to sell it back to issuers?

Putable bonds provide investors with the right to sell the bond back to the issuer at a predetermined price, typically at par value, before the bond reaches its maturity date. This feature is beneficial to investors because it allows them to mitigate the risk of rising interest rates, which can lead to a decrease in bond prices. If interest rates rise and the market value of the bond falls below the putable price, investors can exercise their put option, thus safeguarding their investment's value.

In contrast, convertible bonds allow investors to convert their bonds into equity shares of the issuing company, providing potential upside if the company's stock performs well. Callable bonds, on the other hand, give the issuer the right to redeem the bonds before maturity, which can be disadvantageous to investors if it happens when interest rates drop as they could lose potential income. Mortgage bonds are secured by specific assets, typically real estate, and do not offer a put option to investors. Thus, the unique feature of putable bonds makes them the correct answer, as they specifically grant the right to sell the bonds back to the issuer.