**Core Concept**
Mutarotation is a phenomenon observed in certain sugars, including D-glucose, where the optical rotation changes over time due to the interconversion of anomeric forms (α and β) in solution. This is a fundamental concept in carbohydrate chemistry.

**Why the Correct Answer is Right**
The correct answer is due to the fact that D-glucose exists in two anomeric forms, α-D-glucose and β-D-glucose, which are in equilibrium in aqueous solution. The α-anomer has a positive optical rotation, while the β-anomer has a negative optical rotation. As the equilibrium shifts between these two forms, the net optical rotation of the solution changes, resulting in a change in the observed optical rotation. This phenomenon is known as mutarotation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the phenomenon of mutarotation. Mutarotation is not simply a change in the concentration of D-glucose.
**Option B:** This option is incorrect because it implies that the optical rotation of D-glucose remains constant over time, which is not the case.
**Option C:** This option is incorrect because it does not accurately describe the change in optical rotation that occurs during mutarotation.

**Clinical Pearl / High-Yield Fact**
Mutarotation is an important concept in carbohydrate chemistry and is relevant to the understanding of the behavior of sugars in solution. It is also a classic example of a dynamic equilibrium in chemistry.

**Correct Answer:** A. The optical rotation of a D-glucose solution changes over time due to mutarotation, resulting in a decrease in optical rotation as the α-anomer converts to the β-anomer.