The set representing the correct order of ionic radius is

Options

A. `Na^(+) gt Mg^(2+) gt Al^(3+) gt Li^(+) gt Be^(2+) `
B. `Na^(+) gt Li^(+) gt Mg^(2+) gt Al^(3+) gt Be^(2+) `
C. `Na^(+) gt Mg^(2+) gt Li^(+) gt Al^(3+) gt Be^(2+) `
D. `Na^(+) gt Mg^(2+) gt Li^(+) gt Be^(2+) `

Answer

To determine the correct order of ionic radii among the given elements (Lithium, Beryllium, Sodium, Magnesium, and Aluminium), we need to consider the following factors:

### Step 1: Understand Ionic Radius
The ionic radius is the measure of an atom's ion in a crystal lattice. Cations (positively charged ions) are generally smaller than their parent atoms due to the loss of an electron, which reduces electron-electron repulsion and allows the remaining electrons to be pulled closer to the nucleus.

### Step 2: Consider the Charge of Cations
When comparing cations, the charge on the cation plays a significant role. The greater the positive charge on the cation, the smaller the ionic radius. This is because a higher positive charge increases the effective nuclear charge, pulling the electrons closer to the nucleus.

### Step 3: Analyze the Given Elements
- **Lithium (Li⁺)**: +1 charge
- **Sodium (Na⁺)**: +1 charge
- **Beryllium (Be²⁺)**: +2 charge
- **Magnesium (Mg²⁺)**: +2 charge
- **Aluminium (Al³⁺)**: +3 charge

### Step 4: Compare Ionic Sizes
1. **Lithium vs Sodium**: Both have a +1 charge, but Sodium is larger than Lithium because it is in a higher period (3rd period vs 2nd period).
2. **Beryllium vs Magnesium**: Both have a +2 charge, but Magnesium is larger than Beryllium for the same reason (3rd period vs 2nd period).
3. **Aluminium**: With a +3 charge, Aluminium will be smaller than both Magnesium and Beryllium due to the higher charge.

### Step 5: Order the Ionic Radii
From the analysis:
- **Al³⁺** (smallest)
- **Be²⁺**
- **Mg²⁺**
- **Li⁺**
- **Na⁺** (largest)

Thus, the correct order of ionic radii from smallest to largest is:
**Al³⁺ < Be²⁺ < Mg²⁺ < Li⁺ < Na⁺**

### Conclusion
The correct order of ionic radius among the given elements is represented by the option that corresponds to this sequence.

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