Which one of the following combination of ion will have highest polarisation ?

Options

A. `Pb^(2+) , Br^(-)`
B. `Pb^(4+) , Br^(-)`
C. `Fe^(2+) ,Br^(-)`
D. `Fe^(3+) ,Br^(-)`

Explanation

To determine which combination of ions will have the highest polarization, we will follow these steps:

### Step 1: Understand Polarization
Polarization refers to the distortion of the electron cloud of an anion by a cation. The ability of a cation to polarize an anion is known as its polarizing power.

### Step 2: Apply Fajans' Rule
According to Fajans' rule, the polarizing power of a cation is directly proportional to its charge and inversely proportional to its size. This means:
- Higher charge → Higher polarizing power
- Smaller size → Higher polarizing power

### Step 3: Analyze the Given Cations
We need to compare the cations based on their charges and sizes. Let's denote the cations as follows:
- Cation A: +2 charge, larger size
- Cation B: +4 charge, smaller size
- Cation C: +2 charge, medium size
- Cation D: +1 charge, larger size

### Step 4: Determine Polarizing Power
Now, we will assess the polarizing power of each cation:
- Cation A (+2 charge): Moderate polarizing power due to charge but larger size.
- Cation B (+4 charge): Highest polarizing power due to high charge and relatively smaller size.
- Cation C (+2 charge): Moderate polarizing power due to charge and medium size.
- Cation D (+1 charge): Lowest polarizing power due to low charge and larger size.

### Step 5: Conclusion
Based on the analysis, Cation B with a +4 charge will have the highest polarizing power, which will lead to the highest polarization of the anion.

### Final Answer
The combination of ions that will have the highest polarization is the one with Cation B.

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