Assertion Among two cations of similar size the polarising power of cation with pseudo noble gas configuration is larger than cation with noble gas configuration
Reasoning Polarising power of `Ag^(o+)` is more than `K^(o+)` .

Options

A. If both `(A)` and `(R )` are correct and `(R )` is the correct explanation of `(A)`
B. If both `(A)` and `(R )` are correct and `(R )` is the correct explanation of `(A)`
C. If `(A)` is correct but `(R )` is incorrect
D. If `(A)` is incorrect but `(R )` is correct

Explanation

To solve the question regarding the assertion and reasoning about the polarizing power of cations, we will break it down into clear steps.

### Step 1: Understand the Assertion
The assertion states that among two cations of similar size, the polarizing power of a cation with a pseudo noble gas configuration is larger than that of a cation with a noble gas configuration.

### Step 2: Define Polarizing Power
Polarizing power refers to the ability of a cation to distort the electron cloud of an anion. The greater the charge and the smaller the size of the cation, the higher its polarizing power.

### Step 3: Identify the Cations
In this case, we are comparing two cations:
- **Ag⁺ (Silver cation)**
- **K⁺ (Potassium cation)**

### Step 4: Determine Electronic Configurations
- **Potassium (K)** has an atomic number of 19. Its electronic configuration is:
- K: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹
- When it loses one electron to form K⁺, it achieves a noble gas configuration (Ar): 1s² 2s² 2p⁶ 3s² 3p⁶.

- **Silver (Ag)** has an atomic number of 47. Its electronic configuration is:
- Ag: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹
- When it loses one electron to form Ag⁺, it has the configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰, which is a pseudo noble gas configuration.

### Step 5: Analyze the Polarizing Power
- **Effective Nuclear Charge (Z_eff)**: The polarizing power is influenced by the effective nuclear charge. Silver (Ag⁺) has a higher effective nuclear charge compared to potassium (K⁺) because it has more protons in the nucleus. This leads to a smaller ionic radius for Ag⁺ compared to K⁺.

- Since Ag⁺ has a higher effective nuclear charge and a smaller size, it has a greater polarizing power than K⁺.

### Step 6: Conclusion
Both the assertion and reasoning are correct:
- The assertion is true because Ag⁺ (pseudo noble gas configuration) has a higher polarizing power than K⁺ (noble gas configuration).
- The reasoning is correct as it explains why Ag⁺ has a higher polarizing power due to its higher effective nuclear charge and smaller size.

### Final Answer
Both the assertion and reasoning are correct, and the reasoning is the correct explanation for the assertion.

---