Reduction of hexose A (molecular formula `C_(6)H_(12)O_(6)`) with sodium borohydride gives compound B and C. Compound B is optically inactive, whereas compound C is optically active. Which of the following is compound A?

Options

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

Answer

To determine which hexose (compound A) corresponds to the molecular formula C6H12O6 and fits the given conditions of the problem, we can follow these steps:

### Step 1: Identify the Structure of Hexose A
Hexose A has the molecular formula C6H12O6, which indicates it is a monosaccharide with six carbon atoms. Common hexoses include D-glucose, D-fructose, D-mannose, and D-galactose.

### Step 2: Analyze the Reduction with Sodium Borohydride
Sodium borohydride (NaBH4) is a reducing agent that reduces carbonyl groups (aldehydes and ketones) to alcohols.

### Step 3: Consider the Structures of the Options
1. **D-Fructose**: It is a ketose (contains a ketone group).
- Structure: CH2OH-CO-(CHOH)3-CHO
- Upon reduction, it can form two products:
- **Sorbitol** (optically active)
- **Mannitol** (optically inactive)

2. **D-Glucose**: It is an aldose (contains an aldehyde group).
- Structure: CHO-(CHOH)4-CH2OH
- Upon reduction, it forms only one product, which is optically active.

3. **D-Mannose**: It is also an aldose.
- Structure: Similar to glucose but with different configurations.
- Upon reduction, it forms only one product, which is optically active.

4. **D-Galactose**: It is also an aldose.
- Structure: Similar to glucose but with different configurations.
- Upon reduction, it forms only one product, which is optically active.

### Step 4: Determine the Optical Activity of the Products
- For **D-Fructose**:
- The reduction yields both an optically active compound (sorbitol) and an optically inactive compound (mannitol).

- For **D-Glucose, D-Mannose, and D-Galactose**:
- The reduction yields only optically active products.

### Conclusion
Since compound B is optically inactive and compound C is optically active, the only hexose that fits this description is **D-Fructose**.

### Final Answer
Compound A is **D-Fructose**.

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