Which of the following has the lowest solubility

Options

A. `CaF_(2)`
B. `CaCl_(2)`
C. `CaBr_(2)`
D. `CaI_(2)`

Explanation

To determine which of the given compounds has the lowest solubility, we will analyze the solubility of each calcium halide: CaF2, CaCl2, CaBr2, and CaI2.

### Step-by-Step Solution:

1. **Understanding Solubility**:
- The solubility of ionic compounds in water is influenced by two main factors: hydration energy and lattice energy.
- Hydration energy is the energy released when ions are surrounded by water molecules, while lattice energy is the energy required to separate the ions in a solid ionic compound.

2. **Comparing Lattice Energies**:
- Lattice energy is inversely proportional to solubility. This means that a compound with a higher lattice energy will generally have lower solubility.
- For the compounds given, the lattice energy typically increases with the size of the anion. Thus, we can expect the following trend:
- CaF2 (with F-) has the highest lattice energy due to the small size of the fluoride ion.
- CaCl2 (with Cl-) has lower lattice energy than CaF2.
- CaBr2 (with Br-) has even lower lattice energy than CaCl2.
- CaI2 (with I-) has the lowest lattice energy among them due to the larger iodide ion.

3. **Analyzing Hydration Energies**:
- Hydration energy is directly proportional to the charge density of the ions. Smaller ions with higher charges have higher hydration energies.
- In this case, the hydration energy of Ca2+ is significant, but the halide ions' sizes will also influence the overall solubility.

4. **Conclusion on Solubility**:
- Since CaF2 has the highest lattice energy, it will have the lowest solubility among the given compounds.
- Therefore, the compound with the lowest solubility is **CaF2**.

### Final Answer:
The compound with the lowest solubility is **CaF2**.