Final answer:
The security on a loan that serves in the event of nonpayment is a deed of trust, which provides the lender with a claim against the borrower's property if they default.
Step-by-step explanation:
The security on a loan in the event of nonpayment is typically some form of collateral. This collateral could be property or equipment that the lender has the right to seize and sell to recover the funds lent in case the borrower does not repay the loan. Among the options presented, a) Promissory note, b) Deed of trust, c) Title insurance, and d) Credit report, the one that serves as security on a loan in the event of nonpayment is the deed of trust. A deed of trust involves real estate and serves as security for a loan by providing the lender with a claim against the property if the borrower defaults.