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 determine which disaccharide in acidic medium is called invert sugar, we need to understand the concept of optical activity and the hydrolysis of disaccharides. Here’s a step-by-step solution:

### Step 1: Understand Invert Sugar
Invert sugar is a term used to describe a mixture of glucose and fructose that is formed when sucrose (a disaccharide) is hydrolyzed. Invert sugar has different optical properties compared to the original sugar.

**Hint:** Remember that invert sugar is specifically related to the hydrolysis of sucrose.

### Step 2: Identify the Disaccharides
The common disaccharides include sucrose, lactose, and maltose. Among these, sucrose is the one that is typically hydrolyzed to produce invert sugar.

**Hint:** Focus on the disaccharides that are commonly known and their hydrolysis products.

### Step 3: Hydrolysis of Sucrose
When sucrose is hydrolyzed in an acidic medium, it breaks down into two monosaccharides: glucose (which is dextrorotatory) and fructose (which is levorotatory).

**Hint:** Recall that dextrorotatory sugars rotate plane-polarized light to the right, while levorotatory sugars rotate it to the left.

### Step 4: Optical Activity Before and After Hydrolysis
Before hydrolysis, sucrose is dextrorotatory, meaning it rotates light to the right. After hydrolysis, the resulting mixture of glucose and fructose has a net optical rotation that is levorotatory (rotating light to the left).

**Hint:** Consider how the individual rotations of glucose and fructose combine to give a different overall rotation.

### Step 5: Conclusion
The change in optical activity from dextrorotatory (sucrose) to levorotatory (the mixture of glucose and fructose) is what defines invert sugar. Therefore, the answer to the question is that sucrose is the disaccharide that, when hydrolyzed in acidic medium, is called invert sugar.

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