The correct order of ionic radii of the following species is

Options

A. `Se^(2-) gt I^(-) gt Br^(-) gt O^(2-) gt F^(-)`
B. `I^(-) gt Se^(2-) gt O^(2-) gt F^(-)`
C. `Se^(2-) gt I^(-) gt Br^(-) gt F^(-) gt O^(2-)`
D. `I^(-) gt Se^(2-) gt Br^(-) gt O^(2-) gt F^(-)`

Answer

To determine the correct order of ionic radii for the given species, we need to consider the periodic trends in ionic sizes. Here’s a step-by-step breakdown of how to approach this question:

### Step 1: Identify the Species
We have the following species to compare:
1. O²⁻ (Oxide ion)
2. S²⁻ (Sulfide ion)
3. Se²⁻ (Selenide ion)
4. F⁻ (Fluoride ion)
5. Cl⁻ (Chloride ion)
6. Br⁻ (Bromide ion)
7. I⁻ (Iodide ion)

### Step 2: Understand the Trends in Ionic Radii
- **Down a Group**: As we move down a group in the periodic table, ionic radii increase. This is due to the addition of electron shells, which increases the distance between the nucleus and the outermost electrons.
- **Across a Period**: As we move from left to right across a period, ionic radii generally decrease. This is because the increasing nuclear charge pulls the electrons closer to the nucleus.

### Step 3: Analyze the Anions
1. **Oxygen Family Anions**:
- O²⁻, S²⁻, Se²⁻: As we go down the group from O to Se, the ionic radius increases.
- Order: O²⁻ < S²⁻ < Se²⁻

2. **Halogen Anions**:
- F⁻, Cl⁻, Br⁻, I⁻: Similarly, as we go down the group from F to I, the ionic radius increases.
- Order: F⁻ < Cl⁻ < Br⁻ < I⁻

### Step 4: Compare the Anions from Different Groups
- When comparing anions from different groups, we can see that the size of the anions increases as we go down a group.
- The anions O²⁻, S²⁻, and Se²⁻ will be smaller than the halogen anions F⁻, Cl⁻, Br⁻, and I⁻.

### Step 5: Final Order of Ionic Radii
Combining the information:
- From the oxygen family: O²⁻ < S²⁻ < Se²⁻
- From the halogens: F⁻ < Cl⁻ < Br⁻ < I⁻

Now, we can conclude that:
- The largest anion is I⁻, followed by Br⁻, Cl⁻, F⁻, Se²⁻, S²⁻, and the smallest is O²⁻.

### Final Order of Ionic Radii:
I⁻ > Br⁻ > Cl⁻ > F⁻ > Se²⁻ > S²⁻ > O²⁻