Which one of the following order is correct ?

Options

A. `I gt I^(+) gt I^(-)` (radii)
B. `I^(-) gt I gt I^(+)` (radii)
C. `I^(-) gt I gt I^(+)` (lonisation energy)
D. `I^(+5) lt I^(+) lt I^(+7)` (lonisation energy)

Answer

To solve the question regarding the correct order of sizes of ions and their ionization energies, we need to understand the concepts of cations, anions, and their relationships with their parent atoms. Let's break it down step by step:

### Step 1: Understanding Cations
- **Definition**: Cations are positively charged ions formed when a parent atom loses one or more electrons.
- **Example**: If we take a parent atom A with an electronic configuration of 2, 8, 1, and it loses one electron, it becomes A⁺ (a cation) with an electronic configuration of 2, 8.
- **Size Comparison**: The size of a cation is smaller than its parent atom because losing electrons reduces electron-electron repulsion and the effective nuclear charge experienced by the remaining electrons increases.

### Step 2: Understanding Anions
- **Definition**: Anions are negatively charged ions formed when a parent atom gains one or more electrons.
- **Example**: If we take a parent atom B with an electronic configuration of 2, 7, and it gains one electron, it becomes B⁻ (an anion) with an electronic configuration of 2, 8.
- **Size Comparison**: The size of an anion is larger than its parent atom because gaining electrons increases electron-electron repulsion and the effective nuclear charge remains the same.

### Step 3: Comparing Sizes
- From the above understanding:
- Size order: **Anion (B⁻) > Parent Atom (B) > Cation (A⁺)**
- This means that the anion is larger than the parent atom, which in turn is larger than the cation.

### Step 4: Understanding Ionization Energy
- **Definition**: Ionization energy is the energy required to remove an electron from an atom or ion.
- **Trends**:
- Cations have higher ionization energies than their parent atoms because they have fewer electrons and a higher effective nuclear charge.
- Anions have lower ionization energies than their parent atoms because they have more electrons, which increases electron-electron repulsion.

### Step 5: Evaluating the Options
- Now, let's evaluate the provided options based on our understanding:
1. **Option 1**: Size of parent atom I > I⁺ > I⁻ (Incorrect)
2. **Option 2**: I⁻ > Parent atom I > I⁺ (Correct)
3. **Option 3**: Incorrect based on our analysis.
4. **Option 4**: Incorrect as ionization energy trends do not support this.

### Conclusion
- The correct order concerning size and ionization energy is given by **Option 2**: **I⁻ > Parent atom I > I⁺**.

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