A substance absorbs `CO_2` and violently reacts with water. The substance is

Options

A. `CaCO_3`
B. `CaO`
C. `H_2SO_4`
D. `ZnO`.

Explanation

To determine the substance that absorbs CO2 and reacts violently with water, we can analyze the given options step by step:

### Step 1: Analyze the Options
We have four substances to consider:
1. Calcium Carbonate (CaCO3)
2. Calcium Oxide (CaO)
3. Sulfuric Acid (H2SO4)
4. Zinc Oxide (ZnO)

### Step 2: Evaluate Each Substance
- **Calcium Carbonate (CaCO3)**:
- Calcium carbonate does not react violently with water. It can react with acids but does not absorb CO2 in a way that indicates a violent reaction.

- **Calcium Oxide (CaO)**:
- Calcium oxide is a basic oxide. It reacts violently with water to form calcium hydroxide (Ca(OH)2).
- Additionally, calcium oxide can absorb CO2 from the atmosphere to form calcium carbonate (CaCO3).

- **Sulfuric Acid (H2SO4)**:
- Sulfuric acid is a strong acid and does react violently with water, but it does not absorb CO2. Instead, it can release CO2 when reacting with carbonates.

- **Zinc Oxide (ZnO)**:
- Zinc oxide does not react violently with water. It can react with acids and bases but does not show violent behavior with water.

### Step 3: Conclusion
Based on the evaluations:
- The only substance that absorbs CO2 and reacts violently with water is **Calcium Oxide (CaO)**.

### Final Answer
The substance is **Calcium Oxide (CaO)**.

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