## **Core Concept**
The general sensation to the tongue, including taste and non-taste sensations, is mediated by different cranial nerves. The posterior one-third of the tongue is specifically innervated by a particular nerve for general sensation.

## **Why the Correct Answer is Right**
The correct answer, **Glossopharyngeal nerve (CN IX)**, is responsible for the general sensation (touch, pressure, temperature, and pain) to the posterior one-third of the tongue. This nerve provides the sensory innervation to this specific region. The glossopharyngeal nerve achieves this through its lingual branch.

## **Why Each Wrong Option is Incorrect**
* **Option A: Facial nerve (CN VII)**: This nerve is primarily responsible for taste sensation from the anterior two-thirds of the tongue, not general sensation, and not from the posterior one-third.
* **Option B: Trigeminal nerve (CN V)**: While the trigeminal nerve provides general sensation to the anterior two-thirds of the tongue (via the lingual nerve), it does not innervate the posterior one-third.
* **Option D: Vagus nerve (CN X)**: The vagus nerve provides general sensation to the pharynx and larynx but is not responsible for the sensation to the tongue.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is the innervation of the tongue: the **anterior two-thirds** receive general sensation from the **trigeminal nerve (CN V)** (via the lingual nerve) and taste from the **facial nerve (CN VII)**, while the **posterior one-third** receives both general sensation and taste from the **glossopharyngeal nerve (CN IX)**.

## **Correct Answer:** . Glossopharyngeal nerve