Which of the following carbohydrate is a reducing sugar ?

Options

A. Maltose
B. Glucose
C. Galactose
D. All of above

Answer

To determine which of the following carbohydrates is a reducing sugar, we need to understand the definition and characteristics of reducing sugars.

### Step-by-Step Solution:

1. **Definition of Reducing Sugars**:
Reducing sugars are carbohydrates that can donate electrons or reduce another molecule. This property is typically due to the presence of a free aldehyde or ketone group in their structure.

2. **Identify the Carbohydrates**:
Let's consider the carbohydrates mentioned: maltose, glucose, and galactose.

3. **Structure Analysis**:
- **Glucose**: Glucose is an aldose sugar, which means it has an aldehyde group. In its cyclic form, it has a free hydroxyl (-OH) group on one of the carbons, which allows it to act as a reducing sugar.
- **Galactose**: Similar to glucose, galactose is also an aldose sugar. It has a free hydroxyl group in its structure, making it a reducing sugar as well.
- **Maltose**: Maltose is a disaccharide composed of two glucose units. It has a free reducing end (the glucose unit that is not involved in the glycosidic bond), which allows it to act as a reducing sugar.

4. **Conclusion**:
Since glucose, galactose, and maltose all have free hydroxyl groups or aldehyde groups that can act as reducing agents, they are all reducing sugars.

5. **Final Answer**:
Therefore, the correct answer is that all of the carbohydrates listed (glucose, galactose, and maltose) are reducing sugars.