Which of the following disaccharide in acidic medium is called invert sugar?

Options

A. Lactose
B. Maltose.
C. Sucrose
D. All of these

Answer

To answer the question "Which of the following disaccharides in acidic medium is called invert sugar?", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Invert Sugar**:
- Invert sugar is a mixture of glucose and fructose that is formed when sucrose (table sugar) is hydrolyzed in an acidic medium. The hydrolysis process breaks down sucrose into its constituent monosaccharides.

2. **Identifying the Disaccharide**:
- The disaccharide in question is sucrose (C12H22O11). It is composed of one glucose molecule and one fructose molecule.

3. **Hydrolysis of Sucrose**:
- When sucrose is treated with an acid (like hydrochloric acid) and water, it undergoes hydrolysis:
\[ \text{Sucrose} \xrightarrow{\text{H}^+} \text{Glucose} + \text{Fructose} \]
- This reaction leads to the formation of glucose (C6H12O6) and fructose (C6H12O6).

4. **Optical Activity**:
- Sucrose is dextrorotatory, meaning it rotates plane-polarized light in a clockwise direction. The specific rotation of sucrose is +66.5 degrees.
- Glucose is also dextrorotatory (+52.5 degrees), while fructose is levorotatory, rotating light in the opposite direction (-92 degrees).

5. **Calculating the Resulting Optical Rotation**:
- After hydrolysis, the overall optical rotation can be calculated:
\[ \text{Rotation from Glucose} (+52.5) + \text{Rotation from Fructose} (-92) = -39.5 \text{ degrees} \]
- This means the resultant solution after hydrolysis rotates light in the counterclockwise direction, indicating that it has become levorotatory.

6. **Conclusion**:
- Since the hydrolysis of sucrose in acidic medium results in a solution that rotates plane-polarized light in the opposite direction, it is termed "invert sugar". Therefore, the answer to the question is **sucrose**.

### Final Answer:
The disaccharide in acidic medium that is called invert sugar is **sucrose**.