Which of the following hydroxides is the most soluble in water ?

Options

A. `Mg(OH)_(2)`
B. `Sr(OH)_(2)`
C. `Ca(OH)_(2)`
D. `Ba(OH)_(2)`

Answer

To determine which of the following hydroxides is the most soluble in water, we need to analyze the solubility trends of the hydroxides of alkaline earth metals (Group 2 elements). The hydroxides in question are:

1. Magnesium hydroxide (Mg(OH)₂)
2. Strontium hydroxide (Sr(OH)₂)
3. Calcium hydroxide (Ca(OH)₂)
4. Barium hydroxide (Ba(OH)₂)

### Step-by-Step Solution:

**Step 1: Identify the Group 2 Elements**
- The hydroxides mentioned are derived from alkaline earth metals, which include magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba).

**Step 2: Understand the Solubility Trend**
- In general, the solubility of hydroxides of alkaline earth metals increases as we move down the group from magnesium to barium. This is due to the increase in atomic size and the corresponding decrease in bond strength.

**Step 3: Analyze the Hydroxides**
- Magnesium hydroxide (Mg(OH)₂) is sparingly soluble in water.
- Calcium hydroxide (Ca(OH)₂) has moderate solubility in water.
- Strontium hydroxide (Sr(OH)₂) is more soluble than calcium hydroxide.
- Barium hydroxide (Ba(OH)₂) is highly soluble in water.

**Step 4: Conclusion**
- Based on the trend that solubility increases down the group, barium hydroxide (Ba(OH)₂) is the most soluble hydroxide among the options provided.

### Final Answer:
The most soluble hydroxide in water among the given options is **barium hydroxide (Ba(OH)₂)**.

---