Both alkali metals and alkaline earth metals are `s-`block elements. They resemble each other in many respects but still there are certain dissimilarities in their properties due to different number of electrons in the valence shell, different atomic radii, ionisation enthalpy, electronegativity, etc.
Like lithium, Be also differs from rest of the alkaline earth metals on account of its small atomic size and high electronetativity. `Be^(2+)`ion is very small and exerts a high polarising effect on any anion associated with it.
The solubility in water of sulphates down the group `(darr)` is `BegtMggtCagtSrgtBa`. this si due to

Options

A. Increases in melting point
B. Increases in molecular mass
C. Decreases in lattice enthalpy
D. High heat of solvation for smaller ions

Explanation

To answer the question regarding the solubility of sulfates of alkaline earth metals down the group, we will analyze the factors influencing solubility and the trend observed.

### Step-by-Step Solution:

1. **Understanding the Group Trends**:
- Alkaline earth metals include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). As we move down the group, the atomic size increases.

2. **Charge Density Concept**:
- Charge density is defined as the charge of the ion divided by its volume (size). Smaller ions with the same charge have higher charge density. For example, Be²⁺ has a higher charge density than Ba²⁺ because Be²⁺ is smaller in size.

3. **Hydration Energy**:
- Hydration energy is the energy released when ions are surrounded by water molecules. Smaller ions with higher charge density (like Be²⁺) have greater hydration energy compared to larger ions (like Ba²⁺). This is because they can attract water molecules more effectively.

4. **Trend in Solubility of Sulfates**:
- The solubility of sulfates in water decreases down the group from Be to Ba. This can be attributed to the decreasing hydration energy as the ionic size increases.
- For example, the sulfates of beryllium and magnesium are more soluble in water compared to those of calcium, strontium, and barium.

5. **Conclusion**:
- The decrease in solubility of sulfates down the group is primarily due to the decrease in charge density and hydration energy of the metal ions. As the ionic size increases, the ability of the ions to attract water molecules diminishes, leading to lower solubility.

### Final Answer:
The solubility of sulfates down the group decreases (Be > Mg > Ca > Sr > Ba) due to the decrease in charge density and hydration energy of the metal ions as the size of the ions increases.

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