**Core Concept**
The distance between the tympanic membrane and the medial wall of the middle ear is a critical anatomical measurement that helps in the diagnosis and management of various ear-related disorders. This distance is particularly relevant in the context of otosclerosis, a condition characterized by abnormal bone growth in the middle ear.

**Why the Correct Answer is Right**
The correct answer is based on the anatomical configuration of the middle ear. The middle ear is a small, air-filled cavity located within the petrous part of the temporal bone. It contains three ossicles: the malleus, incus, and stapes. The tympanic membrane, also known as the eardrum, separates the middle ear from the external auditory canal. The medial wall of the middle ear, also known as the promontory, is formed by the promontory bone and contains the oval window, which transmits sound vibrations to the inner ear. The distance between the tympanic membrane and the medial wall of the middle ear at the level of the centre is approximately 1.5 mm, allowing for the proper transmission of sound vibrations.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is too short a distance, which would not allow for proper sound transmission.
**Option B:** This option is incorrect because it is too long a distance, which would lead to conductive hearing loss.
**Option C:** This option is incorrect because it is not a commonly accepted measurement for the distance between the tympanic membrane and the medial wall of the middle ear.

**Clinical Pearl / High-Yield Fact**
In otosclerosis, abnormal bone growth in the middle ear can lead to a reduction in this distance, causing conductive hearing loss. Therefore, accurate measurement of this distance is crucial in diagnosing and managing otosclerosis.

**Correct Answer: C. 1.5 mm**