**Core Concept**
The stapedius muscle is one of the smallest skeletal muscles in the human body, responsible for stabilizing the stapes bone in the middle ear. Its nerve supply is crucial for maintaining proper sound conduction and preventing damage from loud noises.

**Why the Correct Answer is Right**
The stapedius muscle receives its nerve supply from the facial nerve (cranial nerve VII), specifically through its nerve to the stapedius branch. This branch originates from the facial nerve's geniculate ganglion and travels to the stapedius muscle, allowing for precise control over its contraction. The stapedius muscle plays a vital role in the stapedius reflex, which helps protect the ear from loud noises by reducing sound transmission to the inner ear.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the trigeminal nerve primarily supplies the muscles of mastication and some sensory innervation to the face, not the stapedius muscle.
* **Option B:** This option is incorrect because the glossopharyngeal nerve supplies the stylopharyngeus muscle and provides sensory innervation to the pharynx, but not the stapedius muscle.
* **Option D:** This option is incorrect because the vagus nerve has a wide range of functions, including parasympathetic innervation to various organs, but it does not supply the stapedius muscle.

**Clinical Pearl / High-Yield Fact**
The stapedius reflex is an essential protective mechanism that helps prevent damage to the inner ear from loud noises. It is a critical reflex to assess in patients with hearing loss or tinnitus, as abnormalities in this reflex can indicate underlying ear pathology.

**Correct Answer: C. Facial nerve (cranial nerve VII)**