The reducing sugars are called so because they

Options

A. have a free aldehyde group
B. have a free ketone group
C. can change `Cu^(++)" to "Cu^(+)` form
D. cannot be hydrolysed

Answer

### Step-by-Step Solution:

1. **Definition of Reducing Sugars**: Reducing sugars are carbohydrates that can act as reducing agents. This means they have the ability to donate electrons to another substance.

2. **Presence of Functional Groups**: The key characteristic of reducing sugars is the presence of a free aldehyde group (-CHO) or a free ketone group (C=O). These functional groups are essential for the reducing properties.

3. **Chemical Reaction with Copper Ions**: When reducing sugars are mixed with certain reagents, such as Benedict's solution or Fehling's solution, they can reduce copper(II) ions (Cu²⁺) to copper(I) ions (Cu⁺). This reaction is indicative of their reducing ability.

4. **Testing for Reducing Sugars**: The ability of reducing sugars to reduce copper ions is utilized in laboratory tests. When a reducing sugar is present, the blue color of the copper(II) solution changes to a brick-red precipitate, indicating the presence of reducing sugars.

5. **Examples of Reducing Sugars**: Common examples of reducing sugars include glucose, fructose, and galactose. These sugars can be identified due to their ability to reduce copper ions in the testing solutions.

### Conclusion:
Reducing sugars are called so because they have free aldehyde or ketone groups that allow them to act as reducing agents, capable of reducing copper(II) ions to copper(I) ions in specific chemical tests.

---