**Core Concept**
The question is testing the student's knowledge of laryngeal muscles, specifically the muscles responsible for vocal cord movement. The abductor muscles are crucial for opening the glottis, allowing for breathing.

**Why the Correct Answer is Right**
The correct answer is the posterior cricoarytenoid muscle. This muscle is innervated by the recurrent laryngeal nerve and functions to abduct the vocal cords by rotating the arytenoid cartilages laterally. This action increases the distance between the vocal cords, allowing for inhalation and preventing asphyxiation.

**Why Each Wrong Option is Incorrect**
* **Option A:** The thyroarytenoid muscle is actually an adductor of the vocal cords, not an abductor. It helps to shorten and tensify the vocal cords, facilitating voice production.
* **Option B:** The cricothyroid muscle is an intrinsic laryngeal muscle that tenses and elongates the vocal cords, primarily involved in pitch modification.
* **Option C:** The arytenoid muscle (specifically the lateral cricoarytenoid and the transverse arytenoid) is involved in adduction of the vocal cords and also helps in approximation of the arytenoids.

**Clinical Pearl / High-Yield Fact**
The posterior cricoarytenoid muscle is the only abductor of the vocal cords and is essential for maintaining a patent airway. Its paralysis can lead to vocal cord fixation and respiratory distress.

**Correct Answer: C. Posterior cricoarytenoid muscle**