Which of the following salts is insoluble in water at room temperature but soluble in boiling water

Options

A. `CaCl_(2)`
B. `BaCl_(2)`
C. `SrCl_(2)`
D. `PbCl_(2)`

Explanation

To determine which of the given salts is insoluble in water at room temperature but soluble in boiling water, we can analyze the solubility characteristics of each salt mentioned: CaCl2 (Calcium chloride), BaCl2 (Barium chloride), SrCl2 (Strontium chloride), and PbCl2 (Lead(II) chloride).

### Step-by-Step Solution:

1. **Understanding Solubility**:
- At room temperature, some salts may not dissolve well in water, but their solubility can increase significantly when the water is heated. This is due to the increased kinetic energy of the water molecules, which can help to overcome the lattice energy of the salt.

2. **Analyzing Each Salt**:
- **CaCl2 (Calcium chloride)**: This salt is known to be highly soluble in water at both room temperature and boiling water.
- **BaCl2 (Barium chloride)**: Similar to CaCl2, BaCl2 is also soluble in water at room temperature and remains soluble when heated.
- **SrCl2 (Strontium chloride)**: Like the previous two, SrCl2 is soluble in water at room temperature and does not show a significant change in solubility with temperature.
- **PbCl2 (Lead(II) chloride)**: This salt is known to be only slightly soluble in cold water. However, its solubility increases when the water is heated, making it soluble in boiling water.

3. **Conclusion**:
- Among the salts listed, PbCl2 is the only one that is insoluble in water at room temperature but becomes soluble when the water is boiled.

### Final Answer:
The salt that is insoluble in water at room temperature but soluble in boiling water is **PbCl2 (Lead(II) chloride)**.