Sodium sulphate is soluble in water whereas barium sulphate is sparingly soluble because
(a) the hydration energy of `Na_(2)SO_(4)` is less than its lattice energy
(b) the hydration energy of `Na_(2)SO_(4)` is more than its lattice energy
(c) the lattice energy of `BaSO_(4)` is more than its hydration energy
(d) the lattice energy has no role to play in solubility

Options

A. c & b
B. b & c
C. c & d
D. b & d

Answer

To solve the question regarding the solubility of sodium sulfate and barium sulfate in water, we need to analyze the concepts of hydration energy and lattice energy.

### Step-by-Step Solution:

1. **Understanding Hydration Energy**:
- Hydration energy is the energy released when ions are surrounded by water molecules and solvated. A higher hydration energy indicates that the ions are more stabilized in solution.

2. **Understanding Lattice Energy**:
- Lattice energy is the energy required to separate one mole of a solid ionic compound into its gaseous ions. A higher lattice energy indicates that the ions are held together more strongly in the solid state.

3. **Comparing Sodium Sulfate (Na₂SO₄) and Barium Sulfate (BaSO₄)**:
- Sodium sulfate is soluble in water, which means that when it dissolves, the energy released from hydration (hydration energy) must be greater than the energy required to break the ionic bonds in the solid (lattice energy).
- Barium sulfate, on the other hand, is sparingly soluble, indicating that the energy required to break its ionic bonds (lattice energy) is greater than the energy released during hydration.

4. **Conclusion**:
- For sodium sulfate (Na₂SO₄), the hydration energy is greater than the lattice energy, allowing it to dissolve readily in water.
- For barium sulfate (BaSO₄), the lattice energy is greater than the hydration energy, resulting in its low solubility in water.

5. **Choosing the Correct Option**:
- Therefore, the correct answer to the question is:
**(b) the hydration energy of Na₂SO₄ is more than its lattice energy**.