The set representing the correct order of ionic radii is

Options

A. `Li^(+) gt Be^(2+) gt Na^(+) gt Mg^(2+)`
B. `Li^(+) gt Na^(+) gt Mg^(2+) gt Be^(2+)`
C. `Mg^(2+) gt Be^(2 + ) gt Li^(+) gt Na^(+)`
D. `Na^(+) gt Li^(+) gt Mg^(2+) gt Be^(2+)`

Answer

To determine the correct order of ionic radii for the ions Li⁺, Be²⁺, Na⁺, and Mg²⁺, we will analyze the trends in ionic sizes based on their positions in the periodic table.

### Step 1: Understand the Trends in Ionic Radii
- **Ionic Size Trends**: The size of ions is influenced by their charge and their position in the periodic table. Generally, as we move from left to right across a period, ionic size decreases due to increasing nuclear charge, which pulls electrons closer to the nucleus. Conversely, as we move down a group, ionic size increases due to the addition of electron shells.

### Step 2: Identify the Ions and Their Charges
- The ions in question are:
- Li⁺ (Lithium ion)
- Be²⁺ (Beryllium ion)
- Na⁺ (Sodium ion)
- Mg²⁺ (Magnesium ion)

### Step 3: Compare the Ions Based on Their Groups
- **Group 1 (Alkali Metals)**: Li⁺ and Na⁺ belong to Group 1.
- **Group 2 (Alkaline Earth Metals)**: Be²⁺ and Mg²⁺ belong to Group 2.

### Step 4: Analyze the Ionic Sizes
- **Li⁺ vs Na⁺**: Both are in Group 1, but Na⁺ is larger than Li⁺ because it has more electron shells (3 shells for Na⁺ vs 2 for Li⁺).
- **Be²⁺ vs Mg²⁺**: Both are in Group 2, but Mg²⁺ is larger than Be²⁺ for the same reason (3 shells for Mg²⁺ vs 2 for Be²⁺).
- **Comparing Group 1 and Group 2**: Group 1 ions are generally larger than Group 2 ions because Group 1 ions have a single positive charge, while Group 2 ions have a double positive charge, which pulls the electrons closer to the nucleus, resulting in a smaller ionic size.

### Step 5: Establish the Order of Ionic Radii
Based on the above analysis, we can establish the following order of ionic radii from largest to smallest:
1. Na⁺ (largest)
2. Li⁺
3. Mg²⁺
4. Be²⁺ (smallest)

### Final Order
Thus, the correct order of ionic radii is:
**Na⁺ > Li⁺ > Mg²⁺ > Be²⁺**

### Answer
The correct option representing the order of ionic radii is **D**.