Which of the following reagent does not oxidize HCl ?

Options

A. `PbO_(2)`
B. conc. `H_(2)SO_(4)`
C. `MnO_(2)`
D. `K_(2)Cr_(2)O_(7)//H^(-)`

Explanation

To determine which reagent does not oxidize HCl, we will analyze each option provided.

### Step-by-Step Solution:

1. **Identify the nature of HCl**:
- HCl contains Cl⁻ ions, which can act as reducing agents. Cl⁻ is a weak reducing agent, meaning it can be oxidized to Cl₂.

2. **Analyze each reagent**:
- **Option 1: PbO₂ (Lead(IV) oxide)**
- Reaction: PbO₂ + 4HCl → PbCl₂ + 2Cl₂ + 2H₂O
- Conclusion: PbO₂ oxidizes HCl to produce Cl₂.

- **Option 2: Concentrated H₂SO₄ (Sulfuric acid)**
- Reaction: No significant reaction occurs between concentrated H₂SO₄ and HCl.
- Conclusion: Concentrated H₂SO₄ does not oxidize HCl.

- **Option 3: MnO₂ (Manganese dioxide)**
- Reaction: MnO₂ + 4HCl → MnCl₂ + 2Cl₂ + 2H₂O
- Conclusion: MnO₂ oxidizes HCl to produce Cl₂.

- **Option 4: K₂Cr₂O₇ (Potassium dichromate)**
- Reaction: K₂Cr₂O₇ + 14HCl → 2CrCl₃ + 3Cl₂ + 7H₂O
- Conclusion: K₂Cr₂O₇ oxidizes HCl to produce Cl₂.

3. **Final Conclusion**:
- The only reagent that does not oxidize HCl is **Option 2: Concentrated H₂SO₄**.

### Answer:
The reagent that does not oxidize HCl is **Option 2: Concentrated H₂SO₄**.