Which statement is incorrect regarding Lactose?

Options

A. It is composed of `beta`-D(+)-Galactose & `beta`-D(+)-Glucose
B. It is a reducing sugar
C. It is a disaccharides `(C_12H_22O_11)` having eight -OH groups
D. It has glycosidic linkage of `C_1` of glucose & `C_4` OF galactose

Answer

To determine which statement is incorrect regarding lactose, we will analyze the provided options based on the structure and properties of lactose.

### Step-by-Step Solution:

1. **Understanding the Composition of Lactose**:
- Lactose is a disaccharide composed of two monosaccharides: β-D-galactose and β-D-glucose.
- Therefore, any statement claiming that lactose is made up of these two components is correct.

**Hint**: Recall the basic structure of disaccharides and their monomeric units.

2. **Identifying Reducing Sugar**:
- A reducing sugar is one that has a free aldehyde or ketone group capable of acting as a reducing agent.
- In the case of lactose, both β-D-galactose and β-D-glucose have free anomeric hydroxyl groups, making lactose a reducing sugar.

**Hint**: Check for free functional groups in the structure of the sugar to determine if it is reducing.

3. **Counting Hydroxyl Groups**:
- To verify the number of hydroxyl (OH) groups in lactose, we can analyze its structure:
- β-D-galactose has 4 OH groups.
- β-D-glucose has 4 OH groups.
- When combined, we need to consider the glycosidic bond, which connects the two sugars, effectively reducing the total count by one.
- Thus, the total number of OH groups in lactose is 4 (from galactose) + 4 (from glucose) - 1 (due to the bond) = 7 OH groups.

**Hint**: Count the OH groups in each monosaccharide and adjust for the glycosidic bond.

4. **Analyzing Glycosidic Linkage**:
- The glycosidic linkage in lactose occurs between the C1 of β-D-galactose and the C4 of β-D-glucose.
- If any statement claims otherwise, it would be incorrect.

**Hint**: Remember the specific carbons involved in the glycosidic bond when analyzing the structure.

5. **Conclusion**:
- Now, let’s summarize the statements:
1. Lactose is made up of β-D-galactose and β-D-glucose - **Correct**.
2. Lactose is a reducing sugar - **Correct**.
3. Lactose has 8 OH groups - **Incorrect** (it has 7).
4. Lactose has a glycosidic linkage between C1 of glucose and C4 of galactose - **Incorrect** (it is C1 of galactose and C4 of glucose).

- The incorrect statement regarding lactose is that it has 8 OH groups.

### Final Answer:
The incorrect statement regarding lactose is that it has 8 OH groups.