Property of the alkaline earth metals that increases down the group with their atomic number is

Options

A. Solubility of their hydroxides in water
B. Solubility of their sulphates in water
C. Ionization energy
D. Electronegativity

Answer

To solve the question regarding the property of alkaline earth metals that increases down the group with their atomic number, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Group**: The alkaline earth metals belong to Group 2 of the periodic table. This group includes Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), and Barium (Ba).

2. **List the Properties**: The options given are:
- Solubility of hydroxides in water
- Solubility of sulfates in water
- Ionization energy
- Electronegativity

3. **Analyze Ionization Energy and Electronegativity**:
- Ionization energy tends to **decrease** down the group as the atomic size increases.
- Electronegativity also tends to **decrease** down the group for the same reason.

4. **Examine Solubility of Sulfates**:
- The solubility of sulfates in water **decreases** down the group. For example, barium sulfate is less soluble than magnesium sulfate.

5. **Evaluate Solubility of Hydroxides**:
- The solubility of hydroxides in water **increases** down the group. For instance, barium hydroxide is more soluble than magnesium hydroxide.

6. **Understand Lattice Energy and Hydration Energy**:
- Lattice energy refers to the energy required to separate one mole of an ionic solid into its gaseous ions. As we move down the group, the cationic radius increases, leading to a decrease in lattice energy.
- Hydration energy is the energy released when ions are surrounded by water molecules. The decrease in lattice energy is more significant than the increase in hydration energy down the group.

7. **Conclusion**: Since the lattice energy decreases more than the hydration energy increases, the solubility of hydroxides in water increases down the group from beryllium to barium.

### Final Answer:
The property of the alkaline earth metals that increases down the group with their atomic number is the **solubility of their hydroxides in water**.

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