**Core Concept**
Olfaction is the sense of smell mediated by the olfactory epithelium in the nasal cavity. The process involves binding of odorant molecules to olfactory receptors, which triggers a signaling cascade that ultimately leads to the perception of a specific smell.

**Why the Correct Answer is Right**
Olfaction is closely linked to the trigeminal nerve, which is responsible for detecting chemical irritants in the nasal mucosa. The olfactory epithelium is composed of olfactory receptor neurons, supporting cells, and basal cells. These receptor neurons contain cilia that project into the mucus layer, where odorant molecules bind to specific receptors, initiating a signaling pathway that ultimately leads to the perception of a specific smell.

**Why Each Wrong Option is Incorrect**
**Option A:** This statement is true about olfaction.
**Option B:** This statement is true about olfaction.
**Option C:** This statement is true about olfaction.
**Option D:** This statement is false about olfaction. The olfactory epithelium is not located in the nasopharynx.

**Clinical Pearl / High-Yield Fact**
It's essential to note that olfactory dysfunction can be caused by various conditions, including upper respiratory tract infections, head trauma, and neurodegenerative diseases such as Alzheimer's and Parkinson's.

**Correct Answer: D. The olfactory epithelium is not located in the nasopharynx.**