## **Core Concept**
Epimers are carbohydrates that differ in configuration at only one carbon atom. This concept is crucial in understanding the structural differences between various sugars. Glucose is an aldohexose, and its epimers differ at specific carbon positions.

## **Why the Correct Answer is Right**
The correct answer, **C. Galactose**, is the C-4 epimer of glucose. This means that glucose and galactose differ in configuration at the fourth carbon atom (C-4). Glucose has the hydroxyl (-OH) group on C-4 in the down position (or below the plane of the ring in the Haworth projection), while galactose has it in the up position. This single difference in configuration leads to distinct chemical and physical properties.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because it does not specify a known epimer of glucose. Without a structure or name, it's impossible to assess its validity directly, but based on common knowledge, it's not recognized as an epimer.
- **Option B:** This option is incorrect as it does not represent a known sugar or is not identifiable as an epimer of glucose based on provided information.
- **Option D:** This option, Mannose, is an epimer of glucose but at the C-2 position, not C-4. Mannose differs from glucose at the second carbon atom, making it a different epimer.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that epimers have similar chemical properties but can have different biological activities. For example, glucose and galactose are both aldohexoses and are metabolized by the body but through slightly different pathways initially. Galactose is converted into glucose-1-phosphate and then into glucose-6-phosphate before entering glycolysis.

## **Correct Answer:** . Galactose