According to Fajans'rules, the percentage of covalent character in an ionic compound increase if the cation is highly charged or small in size and the anion is large or cation has pseudoinert gas configuration. As a result of the increased covalent character, solubility in less polar solvent increases and the melting point decreases. The correct order of increasing ionic character is

Options

A. `NaCl lt KCl lt RbCl lt CsCl`
B. `NaCl lt KCl lt CsCl lt RbCl`
C. `KCl lt NaCl lt CsCl lt RbCl`
D. `CsCl lt RbCl lt KCl lt NaCl`

Explanation

To determine the correct order of increasing ionic character according to Fajans' rules, we can follow these steps:

### Step 1: Understand Fajans' Rules
Fajans' rules state that the covalent character of an ionic compound increases with:
- Higher charge on the cation
- Smaller size of the cation
- Larger size of the anion

Conversely, this means that the ionic character decreases as the covalent character increases.

### Step 2: Identify the Compounds
Let's assume we are comparing the following salts:
1. NaCl (Sodium Chloride)
2. KCl (Potassium Chloride)
3. RbCl (Rubidium Chloride)
4. CsCl (Cesium Chloride)

### Step 3: Compare Cation Sizes
The sizes of the cations (from smallest to largest) are:
- Na+ < K+ < Rb+ < Cs+

### Step 4: Analyze the Charge
All the compounds listed have the same anion (Cl-) and the same charge (+1) on the cations. Therefore, the charge factor does not vary among these compounds.

### Step 5: Determine Covalent Character
Since covalent character increases with smaller cation size:
- NaCl has the smallest cation (Na+), hence it has the highest covalent character and the lowest ionic character.
- CsCl has the largest cation (Cs+), hence it has the lowest covalent character and the highest ionic character.

### Step 6: Establish the Order of Ionic Character
Based on the analysis:
- NaCl (lowest ionic character)
- KCl
- RbCl
- CsCl (highest ionic character)

Thus, the order of increasing ionic character is:
NaCl < KCl < RbCl < CsCl

### Final Answer
The correct order of increasing ionic character is:
**NaCl < KCl < RbCl < CsCl**

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