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 need to understand the concept of polarization and the factors that influence it.

### Step-by-Step Solution:

1. **Understanding Polarization**:
- Polarization refers to the distortion of the electron cloud of an anion caused by the electric field of a nearby cation. This distortion leads to a shift in the electron density, making the electron cloud unsymmetrical.

2. **Factors Affecting Polarization**:
- **Cation Size**: Smaller cations have a higher polarizing power because they can exert a stronger electric field on the anion due to their concentrated charge.
- **Cation Charge Density**: Cations with a higher charge density (higher charge and smaller size) can polarize anions more effectively.
- **Anion Size**: Larger anions are more easily distorted than smaller ones, as they have a more diffuse electron cloud.

3. **Analyzing the Given Options**:
- We need to evaluate the combinations of cations and anions provided in the question based on their sizes and charges.
- Look for combinations where the cation is small and highly charged, and the anion is large.

4. **Identifying the Best Combination**:
- Among the given options, identify the cation with the highest charge density and the largest anion.
- For example, if the options include cations like \( Li^+ \), \( Na^+ \), and \( Pb^{4+} \), the \( Pb^{4+} \) cation would have the highest polarizing power due to its small size and high charge.

5. **Conclusion**:
- Based on the analysis, the combination of ions with the highest polarization will be the one that includes a small, highly charged cation (like \( Pb^{4+} \)) and a large anion (like \( Br^- \)).

### Final Answer:
The combination of ions that will have the highest polarization is the one with the small, highly charged cation (e.g., \( Pb^{4+} \)) and a large anion (e.g., \( Br^- \)).

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