Correct order of ionic radii among the following is

Options

A. `Na^+ gt Mg^(2+) gt F^(-) gt O^(2-)`
B. `O^(2-) gt F^(-) Mg^(2+) gt Na^(-)`
C. `O^(2-) gt F^(-) gt Na^(+) gt Mg^(2+)`
D. `F^(-) Na^(+) gt Mg^(2+) gt O^(2-)`

Answer

To determine the correct order of ionic radii among the ions Na⁺, Mg²⁺, F²⁻, and O²⁻, we can follow these steps:

### Step 1: Identify the Ions
We have the following ions to compare:
- Na⁺ (Sodium ion)
- Mg²⁺ (Magnesium ion)
- F²⁻ (Fluoride ion)
- O²⁻ (Oxide ion)

### Step 2: Understand Ionic Radii Trends
Ionic radii depend on the charge of the ion and the number of electrons. Generally:
- Cations (positively charged ions) are smaller than their parent atoms because they lose electrons, leading to a decrease in electron-electron repulsion and a greater effective nuclear charge.
- Anions (negatively charged ions) are larger than their parent atoms because they gain electrons, which increases electron-electron repulsion and decreases the effective nuclear charge per electron.

### Step 3: Compare the Ions
1. **Cations**:
- Na⁺ has a +1 charge.
- Mg²⁺ has a +2 charge.
- Between Na⁺ and Mg²⁺, Mg²⁺ will be smaller due to its higher positive charge attracting the electrons more strongly.

2. **Anions**:
- F²⁻ has a -2 charge.
- O²⁻ has a -2 charge.
- Between F²⁻ and O²⁻, both have the same charge but different atomic numbers. O²⁻ will be larger than F²⁻ because it has fewer protons (8 for O compared to 9 for F), leading to a weaker attraction on the added electrons.

### Step 4: Establish the Order
From the above comparisons:
- O²⁻ > F²⁻ (O²⁻ is larger)
- Na⁺ < Mg²⁺ (Mg²⁺ is smaller)
- Therefore, the order from largest to smallest ionic radii is:
O²⁻ > F²⁻ > Na⁺ > Mg²⁺

### Final Order
Thus, the correct order of ionic radii is:
**O²⁻ > F²⁻ > Na⁺ > Mg²⁺**