Which of the following orders of ionic radii is correctly represented ?

Options

A. `H^(-) gt H^(+) gt,H `
B. `Na^(+) gt F gt O^(2)`
C. `O^(2-) gt F^(-) gt Na^(+)`
D. `AI^(3+) gt Mg^(2+) gt N^(3-)`

Answer

To determine the correct order of ionic radii among the given options, we need to understand the concepts of cations, anions, and their respective sizes in relation to their parent atoms. Here’s a step-by-step breakdown of the solution:

### Step 1: Understand Ionic Radii
- **Definition**: Ionic radii refer to the size of ions, which can be either cations (positively charged) or anions (negatively charged).
- **Cations**: When an atom loses electrons to form a cation, it becomes smaller than its parent atom because:
- There are fewer electrons to repel each other.
- The remaining electrons are pulled closer to the nucleus due to increased effective nuclear charge.

- **Anions**: When an atom gains electrons to form an anion, it becomes larger than its parent atom because:
- There are more electrons, leading to increased electron-electron repulsion.
- The nucleus has to hold more electrons, which reduces the effective nuclear charge per electron.

### Step 2: Analyze Isoelectronic Species
- **Isoelectronic Species**: These are ions or atoms that have the same number of electrons. In a series of isoelectronic species, the size order is generally:
- Anion > Parent Atom > Cation.

### Step 3: Evaluate the Given Options
1. **Option 1**: Incorrect because it shows cation larger than the parent atom.
2. **Option 2**: Incorrect because it shows the anion (O²⁻) smaller than the cation (Na⁺).
3. **Option 3**: Correct because it follows the trend: Anion > Parent Atom > Cation.
4. **Option 4**: Incorrect because it shows a cation (Al³⁺) larger than an anion.

### Conclusion
After analyzing the options based on the principles of ionic radii, the correct order of ionic radii is represented in **Option 3**.

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