Sucrose is a non-reducing sugar. Maltose and lactose are reducing sugars. Why ?

Explanation

### Step-by-Step Solution:

1. **Definition of Sugars**: Understand that sugars can be classified into reducing and non-reducing sugars. Reducing sugars have a free aldehyde or ketone group that can donate electrons, while non-reducing sugars do not have these free groups.

2. **Identify the Sugars**: The question mentions three disaccharides: sucrose, maltose, and lactose. We need to analyze the structure of each to determine their reducing properties.

3. **Structure of Sucrose**: Sucrose is composed of glucose and fructose. In sucrose, the glucose unit has an aldehyde group at the first carbon, and the fructose unit has a ketone group at the second carbon. When these two monosaccharides bond to form sucrose, both the aldehyde group of glucose and the ketone group of fructose are involved in forming glycosidic bonds. As a result, neither of these groups is free to act as a reducing agent.

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