Final answer:
Tetracaine is the synthetic local anesthetic effective on mucous membranes and used in ophthalmology.
Step-by-step explanation:
The synthetic local anesthetic that is effective on the mucous membranes and is commonly used as a surface agent in ophthalmology is tetracaine (Choice D). Tetracaine is known for its potency and longer duration of action compared to other local anesthetics. When applied topically, tetracaine numbs the mucous membranes of the eye, thereby allowing for various eye procedures to be performed without causing discomfort to patients.