Which of the following compound is completely water soluble?

Options

A. `BaSO_(4)`
B. `Ba(OH)_(2)`
C. `Al(OH)_(3)`
D. `CaF_(2)`

Explanation

To determine which of the given compounds is completely water soluble, we will analyze each compound based on their solubility in water.

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds given are:
- Barium sulfate (BaSO₄)
- Barium hydroxide (Ba(OH)₂)
- Aluminum hydroxide (Al(OH)₃)
- Calcium fluoride (CaF₂)

2. **Check Solubility of Barium Sulfate (BaSO₄)**:
- Barium sulfate is known to be insoluble in water. It typically forms a white precipitate when mixed with sulfate ions.
- **Conclusion**: Not water soluble.

3. **Check Solubility of Barium Hydroxide (Ba(OH)₂)**:
- Barium hydroxide is an alkaline earth metal hydroxide. Alkaline earth metal hydroxides are generally soluble in water, especially those of barium and calcium.
- **Conclusion**: Water soluble.

4. **Check Solubility of Aluminum Hydroxide (Al(OH)₃)**:
- Aluminum hydroxide is amphoteric and has very low solubility in water. It does not dissolve significantly in water.
- **Conclusion**: Not water soluble.

5. **Check Solubility of Calcium Fluoride (CaF₂)**:
- Calcium fluoride is also known to be sparingly soluble in water. It does not dissolve well and often forms a precipitate.
- **Conclusion**: Not water soluble.

6. **Final Conclusion**:
- Among the four compounds, only **Barium Hydroxide (Ba(OH)₂)** is completely water soluble.

### Answer:
The compound that is completely water soluble is **Barium Hydroxide (Ba(OH)₂)**.