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
Arranfe of the following species in dereasing order of polarising powers `Ag^(o+),TI^(o+),Na^(o+)` .

Options

A. `TI^(o+) gtAg^(o+) gtNa^(o+)`
B. `TI^(o+) gtAg^(o+) gtAg^(o+)`
C. `Ag^(o+) gtTI^(o+) gtNa^(o+)`
D. `Na^(o+) gtTI^(o+) gtAg^(o+)`

Explanation

To determine the decreasing order of polarizing powers for the cations Ag⁺, Tl⁺, and Na⁺, we will follow the guidelines provided by Fajans' rules. Here’s a step-by-step solution:

### Step 1: Identify the electronic configurations of the cations
- **Ag⁺ (Silver cation)**: The atomic number of silver (Ag) is 47. When it loses one electron to form Ag⁺, it has 46 electrons. The electronic configuration is:
- \( \text{Ag}^+: [Kr] 4d^{10} 5s^0 \) or \( [Ar] 3d^{10} 4s^2 4p^6 4d^{10} \)

- **Tl⁺ (Thallium cation)**: The atomic number of thallium (Tl) is 81. When it loses one electron to form Tl⁺, it has 80 electrons. The electronic configuration is:
- \( \text{Tl}^+: [Kr] 4d^{10} 5s^2 5p^6 4f^{14} 5d^{10} 6s^2 6p^0 \)

- **Na⁺ (Sodium cation)**: The atomic number of sodium (Na) is 11. When it loses one electron to form Na⁺, it has 10 electrons. The electronic configuration is:
- \( \text{Na}^+: 1s^2 2s^2 2p^6 \) (which is the configuration of neon, a noble gas)

### Step 2: Analyze the polarizing power based on size and configuration
According to Fajans' rules:
1. **Smaller cations have higher polarizing power**.
2. **Cations with pseudo-noble gas configuration have higher polarizing power than those with noble gas configuration**.

- **Na⁺** has a noble gas configuration (Neon), which gives it the lowest polarizing power.
- **Ag⁺** and **Tl⁺** both have pseudo-noble gas configurations. However, we need to compare their sizes to determine their polarizing power.

### Step 3: Compare the sizes of Ag⁺ and Tl⁺
- **Ag⁺** is in the 5th period, while **Tl⁺** is in the 6th period. Generally, cations in higher periods are larger due to the addition of electron shells.
- Therefore, **Ag⁺** is smaller than **Tl⁺**.

### Step 4: Arrange the cations in decreasing order of polarizing power
Based on the analysis:
- **Ag⁺** has the highest polarizing power (smallest size and pseudo-noble gas configuration).
- **Tl⁺** has a lower polarizing power than Ag⁺ but higher than Na⁺ (larger size but still pseudo-noble gas).
- **Na⁺** has the lowest polarizing power (noble gas configuration).

### Final Order:
The order of polarizing power from highest to lowest is:
1. **Ag⁺**
2. **Tl⁺**
3. **Na⁺**