The instrument, which pledges real property as security for a loan, is:a mortgage. a trust deed. a promissory note. either a mortgage or a trust deed.

The correct answer is Either a mortgage or a trust deed.

Explanation:

First, the mortgage consists of a real guarantee right that is imposed on a real estate in a public deed, whose purpose is to ensure compliance with an obligation. Hence, in case of default of the debtor, the real estate is auctioned off so that the obligation is paid with its amount.

On the other hand, there is the figure of the guarantee trust, which, like the mortgage, is intended to guarantee compliance with an obligation. However, with this, the settlor (debtor) transfers the good to an impartial third party called a fiduciary, in order for the latter to administer it and take care of it as a good parent, and in case there is a breach of the obligation, the trustee may finish off the property at the request of the trustee (creditor), in order to meet its interests.