Final answer:
When administering eye drops, the nurse should instruct the mother to place them in the conjunctival sac, which is formed when the lower lid is pulled down.
Step-by-step explanation:
When teaching a mother how to administer eye drops, the nurse should tell her to place them in the conjunctival sac that is formed when the lower lid is pulled down. The conjunctival sac is the space between the lower eyelid and the eye itself. By placing the eye drops in this area, the medication can easily reach the surface of the eye and be absorbed. Placing the drops anywhere else may not be as effective in delivering the medication to the eye.