The reagent used to convert glucose into saccharic acid is:

Options

A. Ammonium hydroxide
B. Alkaline solution of iondine
C. `Br_2//H_2 O`
D. Nitric acid

Explanation

To convert glucose into saccharic acid, we need to identify the appropriate reagent that can facilitate this transformation. Saccharic acid (also known as glucaric acid) is formed from glucose through oxidation.

### Step-by-Step Solution:

1. **Identify the Structure of Glucose**:
- Glucose is an aldose sugar with the molecular formula C6H12O6. Its structure includes an aldehyde group (-CHO) and multiple hydroxyl groups (-OH).

2. **Understand the Reaction**:
- The conversion of glucose to saccharic acid involves the oxidation of the aldehyde group to a carboxylic acid group (-COOH).

3. **Evaluate the Reagents**:
- **Option 1: Ammonium Hydroxide**: This is not an oxidizing agent and cannot convert glucose to saccharic acid.
- **Option 2: Alkaline Iodine Solution**: This reagent is typically used to oxidize sugars to aldonic acids, not further to saccharic acid.
- **Option 3: Bromine Water**: This is a mild oxidizing agent that can oxidize glucose to gluconic acid, but not to saccharic acid.
- **Option 4: Nitric Acid (HNO3)**: This is a strong oxidizing agent capable of fully oxidizing glucose, converting both the aldehyde group and the primary alcohol groups to carboxylic acids, leading to saccharic acid.

4. **Conclusion**:
- The reagent that can convert glucose into saccharic acid is **Nitric Acid (HNO3)**.

### Final Answer:
The reagent used to convert glucose into saccharic acid is **Nitric Acid (HNO3)**.