Maximum covalent character is associated with the compound

Options

A. NaI
B. `MgI_2 `
C. `"AlCl"_3 `
D. `"AlI"_3 `

Answer

To determine which compound has the maximum covalent character, we can follow these steps:

### Step 1: Understand Fajan's Rule
Fajan's rule states that the covalent character in ionic compounds is influenced by the ionic potential of the cation and anion. The ionic potential is defined as the charge of the ion divided by its size (radius).

### Step 2: Identify the Compounds
The compounds given are:
1. NaI (Sodium Iodide)
2. MgI2 (Magnesium Iodide)
3. AlI3 (Aluminium Iodide)

### Step 3: Analyze the Anions
The anion in all three compounds is iodide (I⁻). Since the size of the iodide ion is the same in all cases, we can focus on the cations to determine the covalent character.

### Step 4: Determine the Charge and Size of Cations
- **Na⁺ (Sodium)**: Charge = +1
- **Mg²⁺ (Magnesium)**: Charge = +2
- **Al³⁺ (Aluminium)**: Charge = +3

### Step 5: Compare the Size of Cations
- Sodium (Na⁺) has a larger ionic radius than Magnesium (Mg²⁺), and Magnesium has a larger ionic radius than Aluminium (Al³⁺). Therefore, the order of size is:
- Na⁺ > Mg²⁺ > Al³⁺

### Step 6: Calculate Ionic Potential
According to Fajan's rule:
- The ionic potential for cations is directly proportional to the charge and inversely proportional to the size.
- Thus, we can summarize:
- For Na⁺: Ionic Potential = +1 / (size of Na⁺)
- For Mg²⁺: Ionic Potential = +2 / (size of Mg²⁺)
- For Al³⁺: Ionic Potential = +3 / (size of Al³⁺)

### Step 7: Determine Maximum Covalent Character
Since the covalent character is higher for cations with higher charge and smaller size, we can conclude:
- Al³⁺ has the highest charge (+3) and the smallest size among the cations considered. Therefore, it will have the maximum covalent character.

### Conclusion
The compound with the maximum covalent character is **AlI3 (Aluminium Iodide)**.

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