**Core Concept**
The external auditory meatus, also known as the ear canal, is a narrow passageway that connects the outer ear to the eardrum. Its length is an important anatomical measurement, relevant for various medical and surgical procedures.

**Why the Correct Answer is Right**
The external auditory meatus is approximately 2.5 cm in length in adults, with a slightly shorter length in children. This measurement is crucial for ear surgery, earwax removal, and the insertion of ear tubes. The length of the external auditory meatus is also relevant for the placement of hearing aids and earplugs.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is too short. The external auditory meatus is longer than 1 cm.
**Option B:** This option is incorrect because it is too long. While there can be some variation in the length of the external auditory meatus, 5 cm is significantly longer than the typical length.
**Option C:** This option is incorrect because it is too short. While the length of the external auditory meatus can vary, 1.5 cm is shorter than the typical length.

**Clinical Pearl / High-Yield Fact**
The length of the external auditory meatus is a useful measurement for clinicians, particularly in the context of ear surgery and earwax removal. It is essential to accurately measure the length of the ear canal to avoid complications and ensure successful treatment outcomes.

**Correct Answer:** C. 2.5 cm.