Which of the following represents an unconditional written promise to pay a certain sum in money?

The correct choice is the promissory note, as it specifically refers to a financial instrument that contains an unconditional written promise to pay a specified amount of money at a designated time or on demand. This means that the borrower agrees to repay the lender the amount specified in the note, providing clear terms regarding the repayment.

A loan agreement, while it may contain promises to repay, typically encompasses a broader arrangement between the lender and borrower, including various terms and conditions such as interest rates, repayment schedules, and other obligations. It is not simply a written promise to pay a specific sum.

A bond is a financial instrument that represents a loan made by an investor to a borrower (typically corporate or governmental), where the borrower promises to pay interest and repay the principal at a later date. While it includes a promise to pay, it is more complex and not as straightforward as a promissory note.

A mortgage is a type of security interest in real property and includes a promise to repay a loan. However, it also encompasses details surrounding the collateral (the property) and is used specifically in the context of real estate financing, making it more than just a simple promise to pay money.

In contrast, the promissory note is unambiguous in its purpose