Which of the following compound does not liberated oxygen gas on warming with conc. `H_(2)SO_(4)` ?

Options

A. `SO_3`
B. `PbO_2`
C. `MnO_2`
D. `CrO_5`

Answer

To determine which compound does not liberate oxygen gas when warmed with concentrated sulfuric acid (H₂SO₄), we will analyze the reactions of each compound with concentrated H₂SO₄.

### Step-by-Step Solution:

1. **Identify the Compounds**: We have four compounds to analyze. Let's denote them as:
- A: SO₂ (Sulfur dioxide)
- B: PbO₂ (Lead dioxide)
- C: MnO₂ (Manganese dioxide)
- D: CrO₅ (Chromium pentoxide)

2. **Reaction of SO₂ with Concentrated H₂SO₄**:
- When SO₂ is warmed with concentrated H₂SO₄, it reacts to form oleum (S₂O₇).
- **Reaction**: SO₂ + H₂SO₄ → S₂O₇ (no oxygen gas is liberated).
- Conclusion: SO₂ does not liberate oxygen gas.

3. **Reaction of PbO₂ with Concentrated H₂SO₄**:
- When PbO₂ is warmed with concentrated H₂SO₄, it produces lead sulfate (PbSO₄), water (H₂O), and oxygen gas (O₂).
- **Reaction**: PbO₂ + H₂SO₄ → PbSO₄ + H₂O + ½ O₂.
- Conclusion: PbO₂ liberates oxygen gas.

4. **Reaction of MnO₂ with Concentrated H₂SO₄**:
- When MnO₂ is warmed with concentrated H₂SO₄, it produces manganese sulfate (MnSO₄), water (H₂O), and oxygen gas (O₂).
- **Reaction**: MnO₂ + H₂SO₄ → MnSO₄ + H₂O + ½ O₂.
- Conclusion: MnO₂ liberates oxygen gas.

5. **Reaction of CrO₅ with Concentrated H₂SO₄**:
- When CrO₅ is warmed with concentrated H₂SO₄, it produces chromium sulfate (Cr₂(SO₄)₃) and liberates oxygen gas (O₂).
- **Reaction**: CrO₅ + H₂SO₄ → Cr₂(SO₄)₃ + O₂.
- Conclusion: CrO₅ liberates oxygen gas.

### Final Conclusion:
From the analysis, the only compound that does not liberate oxygen gas when warmed with concentrated H₂SO₄ is **SO₂**.

### Answer:
**A: SO₂**