`BeSO_(4)` is soluble in water but `BaSO_(4)` is insoluble.
Reason (R ): Lattice enthalpy of `BaSO_(4)` exceeds its hydration enthalpy.

Options

A. If both `(A)` and `(R )` are correct and `(R )` is the correct explanation of `(A)`.
B. If both `(A)` and `(R )` are correct, but `(R )` is not the correct explanation of `(A)`.
C. If `(A)` is correct, but `(R )` is incorrect.
D. If `(A)` is incrrect, but `(R )` is correct.

Answer

To solve the question regarding the solubility of `BeSO4` and `BaSO4` in water, we can break it down into steps:

### Step 1: Understand the Assertion
The assertion states that `BeSO4` is soluble in water while `BaSO4` is insoluble. We need to analyze why this is the case.

**Hint:** Consider the properties of the compounds involved, particularly their lattice energies and hydration energies.

### Step 2: Define Lattice Energy and Hydration Energy
Lattice energy is the energy released when gaseous ions combine to form an ionic solid. Hydration energy is the energy released when ions are surrounded by water molecules and solvated.

**Hint:** Remember that the balance between lattice energy and hydration energy determines the solubility of ionic compounds.

### Step 3: Compare Lattice Energy and Hydration Energy
For a compound to be soluble in water, the hydration energy must be greater than the lattice energy. If the lattice energy is greater than the hydration energy, the compound will be insoluble.

**Hint:** Think about the size and charge of the ions in `BeSO4` and `BaSO4`.

### Step 4: Analyze `BeSO4` and `BaSO4`
- `BeSO4` has smaller beryllium ions (Be²⁺) compared to barium ions (Ba²⁺) in `BaSO4`.
- Smaller ions typically lead to higher lattice energy due to stronger ionic bonds.
- However, the hydration energy for `Be²⁺` is significantly high because of its small size and high charge density, making it more favorable for solvation.

**Hint:** Consider how the size and charge of the metal ions influence their hydration energies.

### Step 5: Conclusion on Solubility
Since the hydration energy of `BeSO4` is greater than its lattice energy, it is soluble in water. In contrast, the lattice energy of `BaSO4` exceeds its hydration energy, leading to its insolubility.

**Hint:** Summarize the relationship between lattice energy and hydration energy for both compounds to conclude their solubility behavior.

### Final Answer
Thus, the assertion is correct: `BeSO4` is soluble in water while `BaSO4` is insoluble. The reason provided is also correct: the lattice enthalpy of `BaSO4` exceeds its hydration enthalpy, which explains its insolubility.

### Summary
- Assertion: `BeSO4` is soluble; `BaSO4` is insoluble.
- Reason: Lattice enthalpy of `BaSO4` exceeds its hydration enthalpy.
- Conclusion: Both assertion and reason are correct, and the reason explains the assertion.