**Core Concept**
The objective lens used in microlaryngoscopy is designed to provide a clear and magnified view of the laryngeal structures. The focal length of the objective lens is critical in determining the working distance and the field of view.

**Why the Correct Answer is Right**
The correct focal length of the objective lens used in microlaryngoscopy is typically 300-400 mm. This allows for a good balance between magnification and working distance, enabling the surgeon to maneuver the endoscope and instruments with ease. The 300-400 mm focal length also provides a reasonable field of view, allowing the surgeon to visualize the entire larynx without having to compromise on magnification.

**Why Each Wrong Option is Incorrect**
**Option A:** This focal length is too short and would result in a very close working distance, making it difficult to maneuver the endoscope and instruments.
**Option B:** This focal length is too long and would result in a reduced magnification, making it difficult to visualize the small structures of the larynx.
**Option C:** This focal length is not typically used in microlaryngoscopy and would result in a suboptimal balance between magnification and working distance.

**Clinical Pearl / High-Yield Fact**
The choice of focal length for the objective lens in microlaryngoscopy depends on the specific procedure being performed and the surgeon's preference. However, a focal length of 300-400 mm is generally considered optimal for most microlaryngoscopic procedures.

**Correct Answer:** C.