Which of the following has highest hydration energy ?

Options

A. `MgCl_(2)`
B. `CaCl_(2)`
C. `BaCl_(2)`
D. `SrCl_(2)`

Explanation

To determine which compound has the highest hydration energy among the given options, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Hydration Energy**: Hydration energy is the energy released when one mole of ions is surrounded by water molecules. It is influenced by the charge of the ion and its size.

2. **Identify the Factors**:
- Hydration energy (He) is directly proportional to the charge of the cation.
- Hydration energy is inversely proportional to the size of the cation.

3. **Analyze the Given Ions**: The ions provided are:
- Mg²⁺
- Ca²⁺
- Sr²⁺
- Ba²⁺

All these ions have the same charge (+2), but their sizes differ.

4. **Order of Ionic Size**: In the alkaline earth metals (Group 2), as we move down the group, the size of the cations increases:
- Mg²⁺ < Ca²⁺ < Sr²⁺ < Ba²⁺

5. **Determine Hydration Energy Order**:
- Since hydration energy is inversely proportional to size, smaller ions will have higher hydration energy. Therefore, the order of hydration energy based on size will be:
- Mg²⁺ > Ca²⁺ > Sr²⁺ > Ba²⁺

6. **Conclusion**: Since Mg²⁺ is the smallest ion among the given options, it will have the highest hydration energy. Thus, the compound containing Mg²⁺, which is MgCl₂, will have the highest hydration energy.

### Final Answer:
- **MgCl₂ has the highest hydration energy.**