Which cranial nerve is responsible for motor function in the pharynx?

The cranial nerve responsible for motor function in the pharynx is the vagus nerve (CN10). The vagus nerve plays a critical role in autonomic functions, and it innervates most of the muscles in the pharynx and larynx, which are essential for swallowing and vocalization.

The glossopharyngeal nerve (CN9) does have a role in the sensory functions of the pharynx and contributes to the gag reflex, but it is not primarily responsible for the motor functions. The spinal accessory nerve (CN11) mostly innervates the sternocleidomastoid and trapezius muscles, and it does not have a role in the motor function of the pharynx. The hypoglossal nerve (CN12) is involved in the motor control of the tongue, but it does not have a direct motor function in the pharynx.

Therefore, the vagus nerve is key for motor activity in the pharynx, making it the correct answer.