Manya, Kartik, Gurnoor and Sheena had arranged the ions `F^(-), Na^(+), O^(2-) and Mg^(2+)` in decreasind orders of their ionic radii.
`"Manya" " " -O^(2-)gtMg^(2+)gtF^(-)gtNa^(+)`
`"Kartik" " " - Mg^(2+) gt Na^(+)gtO^(2-)gt^(-)`
`"Gurnoor" " " -O^(2-)gtF^(-)Na^(+)gtMg^(2+)`
`"Sheema" " " - F^(-) gt Na^(+)gtO^(2-)gtMg^(2+)`
Who had provided the correct order of their decreasing ionic radii ?

Options

A. Manya
B. Kartik
C. Gunoor
D. Sheena

Explanation

To determine the correct order of ionic radii for the ions \( F^{-}, Na^{+}, O^{2-}, \) and \( Mg^{2+} \), we need to consider the charges and the nature of the ions.

### Step-by-step Solution:

1. **Understanding Ionic Radii**:
- Anions (negatively charged ions) are generally larger than cations (positively charged ions) because they have gained electrons, which increases electron-electron repulsion.
- Cations are smaller than their neutral atoms because they have lost electrons, resulting in a greater effective nuclear charge acting on the remaining electrons.

2. **Comparing the Ions**:
- **Anions**:
- \( O^{2-} \) (oxide ion) has a larger radius than \( F^{-} \) (fluoride ion) because it has a higher negative charge, leading to greater electron-electron repulsion.
- **Cations**:
- \( Mg^{2+} \) (magnesium ion) is smaller than \( Na^{+} \) (sodium ion) because \( Mg^{2+} \) has a higher positive charge, pulling its electrons closer to the nucleus.

3. **Arranging the Ions**:
- From the above comparisons, we can arrange the ions in order of decreasing ionic radii:
- \( O^{2-} > F^{-} > Na^{+} > Mg^{2+} \)

4. **Evaluating the Given Orders**:
- **Manya**: \( O^{2-} > Mg^{2+} > F^{-} > Na^{+} \) (Incorrect)
- **Kartik**: \( Mg^{2+} > Na^{+} > O^{2-} > F^{-} \) (Incorrect)
- **Gurnoor**: \( O^{2-} > F^{-} > Na^{+} > Mg^{2+} \) (Incorrect)
- **Sheena**: \( F^{-} > Na^{+} > O^{2-} > Mg^{2+} \) (Incorrect)

5. **Conclusion**:
- None of the students provided the correct order of decreasing ionic radii. The correct order is \( O^{2-} > F^{-} > Na^{+} > Mg^{2+} \).