Which cranial nerves are ONLY Sensory?

The cranial nerve that is classified as purely sensory is CN I, the Olfactory nerve. This nerve is responsible solely for the sense of smell. It transmits sensory information from the nasal cavity, where olfactory receptors detect odor molecules, directly to the olfactory bulb in the brain, thus making it essential for the perception of scents.

In contrast, the other cranial nerves mentioned have functions beyond just sensory roles. For instance, CN II, the Optic nerve, does indeed serve a sensory function as it conveys visual information from the retina to the brain, but it is not exclusively sensory in terms of its overall classification; rather, it's purely sensory.

CN III, the Oculomotor nerve, primarily has motor functions as it controls most of the eye's movements, including the constriction of the pupil and maintaining an open eyelid. CN VII, the Facial nerve, has both sensory and motor components; it is involved in taste sensations from the anterior two-thirds of the tongue and controls muscles for facial expression.

Thus, CN I is the only cranial nerve that exclusively serves a sensory function, making it the correct answer in the context of identifying cranial nerves that are solely employed for sensory purposes.