Which is the correct decreasing order of covalent nature :-

Options

A. `SiCl_(4) gt AlCl_(3) gt ZnCl_(2) gt CaCl_(2) gt MgCl_(2)`
B. `SiCl_(4) gt AlCl_(3) gt MgCl_(2) gt CaCl_(2) gt ZnCl_(2)`
C. `ZnCl_(2) gt SiCl_(4) gt AlCl_(3) gt MgCl_(2) gt CaCl_(2)`
D. `SiCl_(4) gt AlCl_(3) gt ZnCl_(2) gt MgCl_(2) gt CaCl_(2)`

Answer

To determine the correct decreasing order of covalent nature for the given halides, we need to consider two main factors: the charge of the cation and the size of the cation. The covalent character of a compound is directly proportional to the charge of the cation and inversely proportional to the size of the cation.

### Step-by-Step Solution:

1. **Identify the Cations and Their Charges:**
- Silicon (Si) in SiCl₄ has a charge of +4.
- Aluminum (Al) in AlCl₃ has a charge of +3.
- Zinc (Zn) in ZnCl₂ has a charge of +2.
- Magnesium (Mg) in MgCl₂ has a charge of +2.
- Calcium (Ca) in CaCl₂ has a charge of +2.

2. **Determine the Size of the Cations:**
- Among the cations with the same charge (+2), the size of the cations is important. The order of size (from smallest to largest) is:
- Zn²⁺ < Mg²⁺ < Ca²⁺

3. **Evaluate Covalent Character Based on Charge and Size:**
- SiCl₄ (Si⁴⁺) has the highest charge (+4), thus it has the highest covalent character.
- AlCl₃ (Al³⁺) has the second highest charge (+3), so it has the second highest covalent character.
- For ZnCl₂, MgCl₂, and CaCl₂, since they all have the same charge (+2), we consider their sizes:
- Zn²⁺ is the smallest, so ZnCl₂ has the highest covalent character among these three.
- Mg²⁺ is larger than Zn²⁺ but smaller than Ca²⁺, so MgCl₂ has the next highest covalent character.
- Ca²⁺ is the largest, so CaCl₂ has the least covalent character among these three.

4. **Arrange in Decreasing Order of Covalent Character:**
- Based on the evaluations:
- SiCl₄ > AlCl₃ > ZnCl₂ > MgCl₂ > CaCl₂

Thus, the correct decreasing order of covalent nature is:
**SiCl₄ > AlCl₃ > ZnCl₂ > MgCl₂ > CaCl₂**

### Final Answer:
The correct option is **D: SiCl₄ > AlCl₃ > ZnCl₂ > MgCl₂ > CaCl₂**.