Which of the following surgical instruments is used to deliver liquids, such as balanced salt solution (BSS), to the surgical site?

The correct choice is the cannula because this instrument is specifically designed for the delivery of fluids to a surgical site. Cannulas have a hollow structure that allows for the movement of liquids, making them ideal for administering balanced salt solution (BSS) during ophthalmic surgeries. This fluid is critical for maintaining the health of ocular tissues during procedures, as it helps to keep the eye hydrated and maintains intraocular pressure.

Forceps, on the other hand, are primarily used for grasping or holding tissue, rather than delivering liquids. Hemostats are specialized clamps used to control bleeding by occluding blood vessels, and they do not serve the function of fluid delivery. Cautery instruments are designed to coagulate or cut tissue through thermal energy, which is unrelated to the delivery of liquids. Therefore, the cannula is the most appropriate and effective tool for delivering solutions at the surgical site.