The maximum covalent character is shown by

Options

A. `AlCl_3`
B. `MgCl_2`
C. `CsCl`
D. `LaCl_3`

Answer

To determine which compound exhibits the maximum covalent character, we can analyze the given options based on the size of the cations and their charges. The compounds provided are Aluminum chloride (AlCl₃), Magnesium chloride (MgCl₂), Cesium chloride (CsCl), and Lanthanum chloride (LaCl₃).

### Step-by-Step Solution:

1. **Identify the Cations and Anions**:
- All compounds have the same anion, Cl⁻ (chloride).
- The cations are Al³⁺ (Aluminum), Mg²⁺ (Magnesium), Cs⁺ (Cesium), and La³⁺ (Lanthanum).

2. **Consider the Size of the Cations**:
- The size of the cations affects their polarizing power. Smaller cations have a higher charge density, which increases their ability to polarize the anion.
- The order of cation sizes is as follows: Cs⁺ > Mg²⁺ > La³⁺ > Al³⁺. Thus, Al³⁺ is the smallest cation among the options.

3. **Evaluate the Charge of the Cations**:
- The charge of the cations also plays a crucial role in determining covalent character. Higher charges lead to greater polarizing power.
- Al³⁺ has a charge of +3, Mg²⁺ has +2, Cs⁺ has +1, and La³⁺ has +3.

4. **Apply Fajans' Rule**:
- Fajans' rule states that the covalent character of an ionic compound increases with the smaller size of the cation and the higher charge of the cation.
- Al³⁺ has the smallest size and the highest charge among the cations in the given options.

5. **Conclusion**:
- Since Al³⁺ is the smallest cation with the highest charge, it will have the greatest polarizing power, leading to the maximum covalent character in Aluminum chloride (AlCl₃).

### Final Answer:
The compound that shows the maximum covalent character is **Aluminum chloride (AlCl₃)**.