Final answer:
The tuning fork is the instrument used for testing auditory acuity, commonly assessed through the Rinne and Weber tests to evaluate hearing loss.
Step-by-step explanation:
The instrument used to test auditory acuity is the tuning fork. A tuning fork can be utilized in various hearing tests, such as the Rinne and Weber tests, to assess different types of hearing loss. During these tests, the tuning fork is struck and placed at specific locations on the patient's head to evaluate the function of the auditory systems. Compared to other options such as the ophthalmoscope for inspecting the eye, the otoscope for examining the ear canal and eardrum, and the Snellen chart which is used to test visual acuity by presenting letters at a distance of 20 feet, the tuning fork is specifically designed for auditory testing.