**Core Concept**
The **referred pain** of the ear is a complex phenomenon involving the **cranial nerves** and **cervical nerves**. The ear receives sensory innervation from multiple nerves, including the **trigeminal nerve**, **facial nerve**, **glossopharyngeal nerve**, and **vagus nerve**.

**Why the Correct Answer is Right**
The **glossopharyngeal nerve** is responsible for the referred pain of the ear, particularly the inner ear. This nerve has a branch called the **tympanic nerve** or **Jacobson's nerve**, which provides sensory innervation to the middle ear. Stimulation of this nerve can cause referred pain in the ear.

**Why Each Wrong Option is Incorrect**
**Option A:** The **trigeminal nerve** is responsible for facial sensation, including the outer ear, but not the inner ear.
**Option B:** The **facial nerve** controls facial expressions and taste, but does not transmit pain sensation from the ear.
**Option D:** The **vagus nerve** is involved in various functions, including swallowing and voice production, but not ear pain.

**Clinical Pearl / High-Yield Fact**
The **glossopharyngeal nerve** is a key nerve involved in the **referred pain** of the ear, and its stimulation can cause ear pain.

**Correct Answer:** D. Glossopharyngeal nerve