Pair of ions with polarising power

Options

A. `Li^(+), Mg^(2+)`
B. `Li^(+), Na^(+)`
C. `Mg^(2+), Ca^(2+)`
D. `Mg^(2+), K^(+)`

Answer

To determine the pair of ions with similar polarizing power, we need to understand the factors that influence polarizing power. Polarizing power is affected by the charge and size of the ions. Here’s a step-by-step breakdown of how to find the correct pair of ions:

### Step 1: Understand Polarizing Power
Polarizing power refers to the ability of a cation to distort the electron cloud of an anion. It is influenced by two main factors:
- **Charge of the ion**: Higher charge increases polarizing power.
- **Size of the ion**: Smaller size increases polarizing power.

### Step 2: Analyze the Given Options
We have four pairs of ions to consider. We need to analyze each pair based on their charge and size.

### Step 3: Identify the Ions
Let’s denote the ions in the options:
1. Li⁺ and Mg²⁺
2. Na⁺ and Ca²⁺
3. K⁺ and Al³⁺
4. Rb⁺ and Sn²⁺

### Step 4: Compare the Ions
- **Li⁺ (Charge +1, Small size)** and **Mg²⁺ (Charge +2, Small size)**: Both are relatively small ions, and Mg²⁺ has a higher charge, but due to the diagonal relationship in the periodic table, they can exhibit similar polarizing power.

- **Na⁺ (Charge +1, Larger than Li⁺)** and **Ca²⁺ (Charge +2, Larger than Mg²⁺)**: Both are larger than Li⁺ and Mg²⁺, but the difference in size and charge makes their polarizing power different.

- **K⁺ (Charge +1, Larger than Na⁺)** and **Al³⁺ (Charge +3, Smaller than K⁺)**: Al³⁺ has a high charge but is smaller, which may lead to a higher polarizing power than K⁺.

- **Rb⁺ (Charge +1, Larger than K⁺)** and **Sn²⁺ (Charge +2, Size comparable to Al³⁺)**: Rb⁺ is larger and has a lower charge compared to Sn²⁺, leading to different polarizing powers.

### Step 5: Conclusion
From the analysis, the pair with similar polarizing power is **Li⁺ and Mg²⁺** due to their diagonal relationship in the periodic table, which results in a comparable charge-to-size ratio.

### Final Answer
The pair of ions with similar polarizing power is **Li⁺ and Mg²⁺**.

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