in an ionic bond the cation tends to polarise the electron cloud of the anion by pulling electron density towards itself This causes development of covalent character in the ionic bond because the electron density gets localised in between the nuclei The tendency of the cation to bring about the polarisation of the anion is expressed as its polasising power The ability of ion to undergo polarisation is called its polarisability The polarising power of a cation or an anion is decided on the basis of `F` ajans' rules as follows .
(i) The smaller the cation, the higher is its polarising power
(ii) Cations with pseudo-noble gas configuration `(ns^(2)np^(6)nd^(10))` have relatively high polarising power than those with noble gas configuration `(ns^(2) np^(6))`
(iii) The larger the size of the anion, the higher is its polarisability
Choose the correct order of polarisability for the following
`I^(Θ),Br^(Θ),CI^(Θ)F^(Θ)` .

Options

A. `I^(ɵ)gtBr^(ɵ)gtCl^(ɵ)F^(ɵ)`
B. `I^(ɵ)gtBr^(ɵ)=Cl^(ɵ)gtF^(ɵ)`
C. `I^(ɵ)=Br^(ɵ)=Cl^(ɵ)gtF^(ɵ)`
D. `I^(ɵ)=Br^(ɵ)ltCl^(ɵ)=F^(ɵ)`

Explanation

To determine the correct order of polarizability for the anions \( I^- \), \( Br^- \), \( Cl^- \), and \( F^- \), we will follow the principles outlined by Fajans' rules.

### Step-by-Step Solution:

1. **Understanding Polarizability**:
- Polarizability refers to the ability of an ion's electron cloud to be distorted by an external electric field, such as the electric field created by a nearby cation. The larger the ion, the more easily its electron cloud can be distorted.

2. **Applying Fajans' Rules**:
- According to Fajans' rules, the polarizability of an anion increases with its size. This means that larger anions will have a higher polarizability because their outermost electrons are held less tightly by the nucleus.

3. **Comparing the Sizes of the Anions**:
- The anions we are comparing are \( I^- \), \( Br^- \), \( Cl^- \), and \( F^- \).
- In the periodic table, as we move down a group, the atomic size increases due to the addition of electron shells. Therefore, the order of size for these halide ions is as follows:
- \( I^- \) (largest)
- \( Br^- \)
- \( Cl^- \)
- \( F^- \) (smallest)

4. **Determining the Order of Polarizability**:
- Since larger ions have higher polarizability, we can conclude the order of polarizability based on their sizes:
- \( I^- > Br^- > Cl^- > F^- \)

5. **Final Answer**:
- The correct order of polarizability for the anions \( I^- \), \( Br^- \), \( Cl^- \), and \( F^- \) is:
- \( I^- > Br^- > Cl^- > F^- \)