Isoelectronic species have the same number of electrons. This property is not only restricted to atoms but also observed in molecules and ions.
Choose the correct order of radius.

Options

A. `O^(2-) gt F^(-)`
B. `Al^(3+) lt Na^(+)`
C. `Na^(+) lt N^(3-)`
D. All of these.

Answer

To determine the correct order of radius for isoelectronic species, we need to analyze the relationship between the charge of the ions and their sizes. Here’s a step-by-step solution:

### Step 1: Identify the Isoelectronic Species
Isoelectronic species are atoms, ions, or molecules that have the same number of electrons. For example, consider the following species:
- O²⁻ (8 protons, 10 electrons)
- F⁻ (9 protons, 10 electrons)
- Ne (10 protons, 10 electrons)
- Na⁺ (11 protons, 10 electrons)
- Mg²⁺ (12 protons, 10 electrons)

### Step 2: Understand the Effect of Charge on Size
The size of ions is influenced by their charge:
- Anions (negatively charged ions) are larger than their neutral atoms because they have gained electrons, which increases electron-electron repulsion.
- Cations (positively charged ions) are smaller than their neutral atoms because they have lost electrons, resulting in a greater effective nuclear charge acting on the remaining electrons, pulling them closer to the nucleus.

### Step 3: Compare Sizes Based on Charge
Given the species listed:
- O²⁻ has the least protons (8) and the most electrons (10), making it the largest.
- F⁻ has 9 protons and 10 electrons, making it smaller than O²⁻ but larger than Ne.
- Ne has 10 protons and 10 electrons, making it smaller than F⁻.
- Na⁺ has 11 protons and 10 electrons, making it smaller than Ne.
- Mg²⁺ has 12 protons and 10 electrons, making it the smallest.

### Step 4: Establish the Order of Radius
From the analysis above, we can establish the order of radius from largest to smallest:
- O²⁻ > F⁻ > Ne > Na⁺ > Mg²⁺

### Final Order:
Thus, the correct order of radius for the given isoelectronic species is:
**O²⁻ > F⁻ > Ne > Na⁺ > Mg²⁺**