Which of the following `N^(3-) , O^(2-) , F^(-)` is largest in size ?

Options

A. ` N^(3-)`
B. `O^(2-)`
C. `F^(-)`
D. All of these

Answer

To determine which of the ions \( N^{3-} \), \( O^{2-} \), and \( F^{-} \) is the largest in size, we can follow these steps:

### Step 1: Identify the Ions and Their Electron Counts
- **Nitrogen (N)** has an atomic number of 7, so in the ion \( N^{3-} \), it has \( 7 + 3 = 10 \) electrons.
- **Oxygen (O)** has an atomic number of 8, so in the ion \( O^{2-} \), it has \( 8 + 2 = 10 \) electrons.
- **Fluorine (F)** has an atomic number of 9, so in the ion \( F^{-} \), it has \( 9 + 1 = 10 \) electrons.

### Step 2: Determine the Number of Protons
- The number of protons corresponds to the atomic number:
- \( N^{3-} \): 7 protons
- \( O^{2-} \): 8 protons
- \( F^{-} \): 9 protons

### Step 3: Understand Isoelectronic Species
Since all three ions have the same number of electrons (10), they are classified as isoelectronic species.

### Step 4: Analyze the Relationship Between Protons and Size
In isoelectronic species, the size of the ions is inversely related to the number of protons. This means:
- More protons result in a stronger nuclear charge, pulling the electrons closer and resulting in a smaller ion.
- Fewer protons result in a weaker nuclear charge, allowing the electrons to be held less tightly, resulting in a larger ion.

### Step 5: Compare the Sizes Based on Proton Count
- \( N^{3-} \) has 7 protons (least nuclear charge).
- \( O^{2-} \) has 8 protons.
- \( F^{-} \) has 9 protons (most nuclear charge).

### Conclusion
Since \( N^{3-} \) has the least number of protons, it will be the largest in size among the three ions. Therefore, the answer is:
\[ N^{3-} \text{ is the largest in size.} \]

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