Invert sugar is an equimolar mixture of d-glucose and :

Options

A. D-galactose
B. D-mannose
C. D-fructose
D. D-ribose

Explanation

To solve the question "Invert sugar is an equimolar mixture of D-glucose and:", we can follow these steps:

### Step 1: Understand Invert Sugar
Invert sugar is defined as a mixture that results from the hydrolysis of sucrose. During this process, sucrose (table sugar) is broken down into its constituent monosaccharides.

**Hint:** Invert sugar is related to the hydrolysis of sucrose.

### Step 2: Identify the Components of Invert Sugar
When sucrose undergoes hydrolysis, it yields two specific monosaccharides: D-glucose and D-fructose.

**Hint:** Remember that hydrolysis of sucrose produces two types of sugars.

### Step 3: Analyze the Optical Activity
Before hydrolysis, sucrose is dextrorotatory (it rotates plane-polarized light to the right). After hydrolysis, the resulting mixture of D-glucose (which is also dextrorotatory) and D-fructose (which is levorotatory) results in an overall change in optical activity, hence the name "invert" sugar.

**Hint:** The optical rotation changes after hydrolysis, leading to the term "invert."

### Step 4: Evaluate the Options
Given the options:
- D-galactose: Incorrect, as it is not produced from sucrose.
- D-mannose: Incorrect, as it is also not produced from sucrose.
- D-fructose: Correct, as it is one of the products of sucrose hydrolysis.

**Hint:** Check each option against what is produced from sucrose hydrolysis.

### Conclusion
The correct answer to the question is that invert sugar is an equimolar mixture of D-glucose and **D-fructose**.

**Final Answer:** D-fructose