Which action is performed to test cranial nerve V (trigeminal nerve)?

The action of clenching teeth is an effective way to test cranial nerve V, also known as the trigeminal nerve. This nerve is primarily responsible for sensation in the face and motor functions such as biting and chewing. By asking the individual to clench their teeth, you can assess the strength and function of the muscles of mastication, which are innervated by the trigeminal nerve. Additionally, you can check for any asymmetry in muscle movement, which could indicate a dysfunction in the nerve.

While the other options involve different cranial nerves, clenching the teeth directly examines the specific muscles and sensory pathways associated with the trigeminal nerve, making it the appropriate choice for testing this cranial nerve.