Which of the following is not oxidized by aqueous `Br_2` ?

Options

A. D - fructose and D - ribulose
B. D - galactose and D - erythrulose
C. D - mannose and d - fructose
D. D - glucose and d - ribose

Answer

To determine which of the following sugars is not oxidized by aqueous bromine, we need to analyze the structure of the sugars provided in the options. Aqueous bromine is a weak oxidizing agent and primarily oxidizes aldehyde groups (CHO) present in sugars.

### Step-by-Step Solution:

1. **Identify the types of sugars:**
- We have two types of sugars: aldoses (which contain an aldehyde group) and ketoses (which contain a ketone group).
- Aldoses can be oxidized by weak oxidizing agents like aqueous bromine, while ketoses generally cannot.

2. **List the sugars in the options:**
- Option 1: D-fructose and D-ribulose (both are ketoses)
- Option 2: D-galactose and D-erythrolose (both are aldoses)
- Option 3: D-mannose and D-fructose (D-mannose is an aldose, D-fructose is a ketose)
- Option 4: D-glucose and D-ribose (D-glucose is an aldose, D-ribose is an aldose)

3. **Analyze each option:**
- **Option 1 (D-fructose and D-ribulose):** Both are ketoses and cannot be oxidized by aqueous bromine.
- **Option 2 (D-galactose and D-erythrolose):** Both are aldoses and can be oxidized.
- **Option 3 (D-mannose and D-fructose):** D-mannose can be oxidized (aldose), but D-fructose cannot (ketose).
- **Option 4 (D-glucose and D-ribose):** Both can be oxidized as they are aldoses.

4. **Conclusion:**
- The only option where both sugars cannot be oxidized by aqueous bromine is **Option 1: D-fructose and D-ribulose**.

Thus, the answer is **D-fructose and D-ribulose**.