In which of the following pairs both the species have nearly the same size ?

Options

A. `K^(+) F^(-)`
B. `Rb^(+) ,O^(2-)`
C. `Li^(+) ,Mg^(2+)`
D. `Mg^(2+) ,A1^(3+)`

Explanation

To determine which pairs of species have nearly the same size, we will analyze the ionic sizes of the given species. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand the Question
We need to find pairs of ions that have similar ionic radii. Ionic size is important because it helps us understand the properties of ions and their interactions.

**Hint:** Look for the ionic radii values of the ions in each pair.

### Step 2: Gather Ionic Radii Values
We will collect the ionic radii values for the ions in each pair provided in the question.

1. **K⁺ (Potassium ion)**: Approximately 133 picometers (pm)
2. **F⁻ (Fluoride ion)**: Approximately 136 picometers (pm)

3. **Rb⁺ (Rubidium ion)**: Approximately 147 picometers (pm)
4. **O²⁻ (Oxide ion)**: Approximately 140 picometers (pm)

5. **Mg²⁺ (Magnesium ion)**: Approximately 65 picometers (pm)
6. **H⁻ (Hydride ion)**: Approximately 60 picometers (pm)

7. **Mg²⁺ (Magnesium ion)**: Approximately 65 picometers (pm)
8. **Al³⁺ (Aluminum ion)**: Approximately 50 picometers (pm)

### Step 3: Compare the Sizes
Now, we will compare the sizes of the ions in each pair to see which ones are nearly the same.

1. **K⁺ and F⁻**:
- K⁺ = 133 pm
- F⁻ = 136 pm
- Difference = 3 pm (nearly the same)

2. **Rb⁺ and O²⁻**:
- Rb⁺ = 147 pm
- O²⁻ = 140 pm
- Difference = 7 pm (nearly the same)

3. **Mg²⁺ and H⁻**:
- Mg²⁺ = 65 pm
- H⁻ = 60 pm
- Difference = 5 pm (nearly the same)

4. **Mg²⁺ and Al³⁺**:
- Mg²⁺ = 65 pm
- Al³⁺ = 50 pm
- Difference = 15 pm (not nearly the same)

### Step 4: Identify the Correct Pairs
From our comparisons, we can conclude:
- Pairs with nearly the same size:
- K⁺ and F⁻
- Rb⁺ and O²⁻
- Mg²⁺ and H⁻

- Pair that does not have nearly the same size:
- Mg²⁺ and Al³⁺

### Final Answer
The pairs in which both species have nearly the same size are:
- K⁺ and F⁻
- Rb⁺ and O²⁻
- Mg²⁺ and H⁻