**Core Concept**
Unilateral palsy of the external laryngeal nerve results from damage to the nerve that supplies the cricothyroid muscle. The external laryngeal nerve is a branch of the superior laryngeal nerve, which originates from the vagus nerve (cranial nerve X). The cricothyroid muscle is responsible for tensing the vocal cords, thereby increasing pitch.

**Why the Correct Answer is Right**
When the external laryngeal nerve is damaged, the cricothyroid muscle becomes paralyzed, leading to a reduction in vocal cord tension. This results in a hoarse or breathy voice, typically with a lower pitch. The affected individual may also experience a decrease in vocal range. The cricothyroid muscle plays a crucial role in adjusting vocal pitch, and its paralysis affects the quality and tone of the voice.

**Why Each Wrong Option is Incorrect**
**Option A:** Unilateral palsy of the external laryngeal nerve does not affect the vocal cord's position or mobility, as this is primarily controlled by the posterior cricoarytenoid muscle, which is innervated by the recurrent laryngeal nerve.
**Option B:** The internal laryngeal nerve, another branch of the superior laryngeal nerve, is responsible for sensory innervation of the laryngeal mucosa and is not directly involved in vocal cord tension or pitch regulation.
**Option C:** The recurrent laryngeal nerve is responsible for innervating all intrinsic laryngeal muscles except the cricothyroid, and its palsy would result in vocal cord paralysis or weakness, not a specific decrease in pitch.
**Option D:** The superior laryngeal nerve's palsy would result in a loss of sensation to the laryngeal mucosa, as well as a decrease in vocal cord tension due to the paralysis of the cricothyroid muscle, but this is not a direct result of unilateral palsy of the external laryngeal nerve alone.

**Clinical Pearl / High-Yield Fact**
It's essential to differentiate between the symptoms of external laryngeal nerve palsy and those of recurrent laryngeal nerve palsy, as the latter can lead to more severe vocal cord dysfunction and potentially life-threatening complications.

**Correct Answer: A. Unilateral palsy of the external laryngeal nerve leads to a decrease in vocal cord tension, resulting in a hoarse or breathy voice, typically with a lower pitch.**