Which one of the following is smallest in size?

Options

A. `N^(3-)`
B. `O^(3-)`
C. `F^-`
D. `Na^+`

Answer

To determine which of the given ions is the smallest in size, we need to understand the relationship between the charge of an ion and its size. Here's a step-by-step solution:

### Step 1: Understand the Types of Species
We have three types of species to consider: cations (positively charged ions), anions (negatively charged ions), and neutral atoms. The size order generally follows:
- Cations < Neutral Atoms < Anions

### Step 2: Analyze the Effect of Charge on Size
- **Cations**: When an atom loses electrons to form a cation, it has fewer electrons than protons. This results in a stronger attraction between the remaining electrons and the nucleus, pulling the electron cloud closer and reducing the size.
- **Anions**: When an atom gains electrons to form an anion, the increased number of electrons leads to greater electron-electron repulsion, causing the electron cloud to expand and increasing the size.
- **Neutral Atoms**: The size of neutral atoms is intermediate between cations and anions.

### Step 3: Compare the Given Ions
Assuming we are comparing specific ions (e.g., \(N^{3-}\), \(Na^{+}\), etc.), we can apply the size order:
- For example, if we have \(N^{3-}\) (an anion) and \(Na^{+}\) (a cation), we can conclude that \(N^{3-}\) will be larger than \(Na^{+}\) because anions are larger than cations.

### Step 4: Identify the Smallest Ion
From our analysis:
- The cation \(Na^{+}\) will be smaller than the anion \(N^{3-}\).
- If there are other cations present, we need to compare their sizes as well. However, generally, cations will be smaller than their neutral counterparts and anions.

### Conclusion
Based on the above reasoning, the smallest ion among the given options is \(Na^{+}\).

### Final Answer
**The smallest ion is \(Na^{+}\).**

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