Which of these salts exhibits the highest melting point?

Options

A. `BeCl_2 `
B. `MgCl_2 `
C. `CaCl_2 `
D. `SrCl_2 `

Answer

To determine which of the given salts exhibits the highest melting point, we will analyze the salts based on their chemical composition and the periodic properties of the elements involved. The salts in question are BeCl2, MgCl2, CaCl2, and SrCl2.

### Step-by-Step Solution:

1. **Identify the Elements**:
The salts consist of the following elements:
- Be (Beryllium)
- Mg (Magnesium)
- Ca (Calcium)
- Sr (Strontium)
All these elements belong to Group 2 of the periodic table, known as the alkaline earth metals.

2. **Understand Melting Point Trends**:
- **Periodicity**: As we move from left to right across a period, the melting point generally increases.
- **Group Trends**: As we move down a group (from Be to Sr), the melting point generally decreases. This is due to the increasing size of the metal ions, which results in a larger distance between the bonding electrons and the positive nucleus, thereby reducing the overall attraction.

3. **Analyze Each Salt**:
- **BeCl2 (Beryllium Chloride)**: Beryllium has a relatively small ionic radius, leading to strong ionic bonds.
- **MgCl2 (Magnesium Chloride)**: Magnesium is larger than beryllium but still has a significant charge density, leading to strong ionic interactions.
- **CaCl2 (Calcium Chloride)**: Calcium is larger than magnesium, which results in weaker ionic interactions compared to MgCl2.
- **SrCl2 (Strontium Chloride)**: Strontium is the largest among these elements, leading to the weakest ionic interactions.

4. **Compare the Melting Points**:
- Based on the trends and the analysis of ionic interactions, we can conclude that:
- BeCl2 has a high melting point due to strong ionic bonds but is still lower than MgCl2.
- MgCl2 has the highest melting point among the four salts due to its relatively small size and high charge density, which results in stronger ionic bonds.
- CaCl2 and SrCl2 have lower melting points due to the increasing size of the metal ions, which weakens the ionic bonds.

5. **Conclusion**:
Therefore, the salt that exhibits the highest melting point is **MgCl2 (Magnesium Chloride)**.