The "smell test" is used to assess which cranial nerve?

The "smell test" specifically assesses the olfactory nerve, which is cranial nerve I. This nerve is responsible for the sense of smell. During the test, an individual is usually asked to close their eyes, block one nostril, and sniff a familiar scent, such as vanilla or coffee. A normal response would indicate the intact function of the olfactory nerve.

The other cranial nerves listed do not play a direct role in the sense of smell. The hypoglossal nerve, for example, is primarily involved in the movement of the tongue, while the vagus nerve has a broader role in autonomic functions, including heart rate and digestion. The trigeminal nerve is primarily associated with sensation in the face and motor functions such as biting and chewing and does not contribute to olfactory perception. Thus, the olfactory nerve is the correct answer for assessing the ability to smell.