Slaked lime reacts slowly with CO2, in air to form a thin layer of.

Options

A. `Ca(HCO_(3))_(2)`
B. CaO
C. `Ca(OH)_(2)`
D. `CaCO_(3)`

Explanation

To solve the question regarding the reaction of slaked lime (calcium hydroxide) with carbon dioxide in the air, we can follow these steps:

### Step-by-Step Solution:

1. **Identify Slaked Lime**:
- Slaked lime is chemically known as calcium hydroxide, represented as \( \text{Ca(OH)}_2 \).

2. **Reaction with Carbon Dioxide**:
- When slaked lime reacts with carbon dioxide (\( \text{CO}_2 \)) present in the air, the following chemical reaction occurs:
\[ \text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O} \]
- This reaction produces calcium carbonate (\( \text{CaCO}_3 \)) and water.

3. **Formation of Thin Layer**:
- Calcium carbonate is known to be insoluble in water. When it forms, it precipitates out of the solution, leading to the formation of a thin layer.
- The calcium carbonate precipitate appears as a white solid, which can create a visible layer.

4. **Conclusion**:
- The thin layer formed as a result of the reaction between slaked lime and carbon dioxide is calcium carbonate (\( \text{CaCO}_3 \)).
- Therefore, the correct answer to the question is option 4: \( \text{CaCO}_3 \).