**Core Concept**
Rhodopsin is a type of visual pigment found in the photoreceptor cells of the retina, specifically in the rod cells. It plays a crucial role in low-light vision by converting light into an electrical signal that can be interpreted by the brain. Rhodopsin is composed of a protein called opsin and a covalently bound molecule called retinal.

**Why the Correct Answer is Right**
The correct answer is a component of the visual pigment rhodopsin because it is one of the two main parts that make up the molecule. Opsin is a protein that provides a binding site for the retinal molecule, while retinal is a derivative of vitamin A that absorbs light and triggers a conformational change in the opsin protein. This change initiates a signaling cascade that ultimately leads to the transmission of visual information to the brain.

*Option A* is incorrect because it is not a component of rhodopsin.
*Option B* is incorrect because it is not a component of rhodopsin; in fact, it is a different type of visual pigment found in cone cells.
*Option D* is incorrect because it is not a component of rhodopsin; it is actually a different type of molecule involved in the visual cycle.

**Clinical Pearl / High-Yield Fact**
Rhodopsin is sensitive to light, which means that it can be bleached by prolonged exposure to bright light. This can lead to a condition called night blindness, where the ability to see in low light is impaired. The visual cycle, which involves the regeneration of rhodopsin, is an important process that helps to maintain normal vision.

**Correct Answer:** C. Retinal.