Identify the correct statement about lactose.

Options

A. It consists of one galactose and one glucose unit
B. Mutarotation is not possible
C. Anomeric carbon of galactose is attached to 4' carbon of glucose which is `beta`-1,4' glycoside bond.
D. Lactase is not used to cleave the `beta-1,4'`-glycoside bond.

Explanation

To identify the correct statement about lactose, we will analyze each statement provided in the question.

### Step 1: Analyze the first statement
**Statement 1:** "It consists of one galactose and one glucose unit."
- Lactose is a disaccharide composed of two monosaccharides: galactose and glucose. When lactose is hydrolyzed, it breaks down into one molecule of galactose and one molecule of glucose.

**Conclusion:** This statement is correct.

### Step 2: Analyze the second statement
**Statement 2:** "Mutarotation is not possible."
- Mutarotation refers to the change in optical rotation due to the interconversion between anomers (α and β forms) of a sugar. Lactose has a free aldehyde group (anomeric carbon) that allows it to undergo mutarotation.

**Conclusion:** This statement is incorrect.

### Step 3: Analyze the third statement
**Statement 3:** "The anomeric carbon of galactose is attached to the 4-carbon of glucose which is a beta-1,4-glycoside bond."
- In lactose, the anomeric carbon of glucose (not galactose) is involved in the glycosidic bond. The bond formed is a β-1,4-glycosidic bond where the anomeric carbon of glucose is attached to the 4th carbon of galactose.

**Conclusion:** This statement is incorrect.

### Final Summary:
- **Correct Statement:** The first statement is correct: "It consists of one galactose and one glucose unit."
- **Incorrect Statements:** The second and third statements are incorrect.