Correct order of solubility

Options

A. `Be(oH)_(2) lt Mg(oH)_(2) lt Ca(oH)_(2) lt Sr(oH)_(2) lt Ba(oH)_(2)`
B. `Mg(oH)_(2) lt Be(oH)_(2) lt Ca(oH)_(2) lt Sr(oH)_(2) lt Ba(oH)_(2)`
C. `Be(oH)_(2) lt Sr(oH)_(2) lt Ca(oH)_(2) lt Mg(oH)_(2) lt Ba(oH)_(2)`
D. `Ba(oH)_(2) lt Mg(oH)_(2) lt Ca(oH)_(2) lt Sr(oH)_(2) lt Be(oH)_(2)`

Answer

To determine the correct order of solubility of the hydroxides of the second group elements (alkaline earth metals), we will analyze the factors affecting solubility and apply them step by step.

### Step-by-Step Solution:

1. **Identify the Elements**: The second group elements (alkaline earth metals) include Beryllium (Be), Magnesium (Mg), Calcium (Ca), and Strontium (Sr).

2. **Understand Solubility Trends**: The solubility of hydroxides in water generally increases as we move down the group from Be to Sr. This is due to the interplay between lattice energy and hydration enthalpy.

3. **Lattice Energy vs. Hydration Enthalpy**:
- **Lattice Energy**: This is the energy required to separate one mole of a solid ionic compound into its gaseous ions. As the size of the metal ion increases down the group, the lattice energy decreases.
- **Hydration Enthalpy**: This is the energy released when gaseous ions are surrounded by water molecules. As the size of the metal ion increases, the hydration enthalpy also decreases.

4. **Analyze the Trends**:
- Beryllium hydroxide (Be(OH)₂) is less soluble because it has a high lattice energy relative to its hydration enthalpy.
- Magnesium hydroxide (Mg(OH)₂) is also less soluble, but more than Be(OH)₂.
- Calcium hydroxide (Ca(OH)₂) is more soluble than both Be(OH)₂ and Mg(OH)₂.
- Strontium hydroxide (Sr(OH)₂) is the most soluble among these hydroxides.

5. **Order of Solubility**: Based on the above analysis, the order of solubility of the hydroxides from least to most soluble is:
- Be(OH)₂ < Mg(OH)₂ < Ca(OH)₂ < Sr(OH)₂

6. **Conclusion**: The correct order of solubility of the hydroxides of the second group elements is:
- **Be(OH)₂ < Mg(OH)₂ < Ca(OH)₂ < Sr(OH)₂**