Which of the following atom or ions has the smallest size?

Options

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

Answer

To determine which of the given atoms or ions has the smallest size, we will follow these steps:

### Step 1: Identify the Atoms/Ions
Let's assume we are comparing the following:
- Nitrogen (N)
- Oxygen (O)
- Fluorine (F)
- Fluoride ion (F⁻)

### Step 2: Understand Atomic Size Trends
Atomic size generally decreases across a period from left to right due to increasing nuclear charge, which pulls the electrons closer to the nucleus. Therefore, we can expect that among nitrogen, oxygen, and fluorine, fluorine will have the smallest atomic size.

### Step 3: Compare the Neutral Atoms
- **Nitrogen (N)** has an atomic number of 7.
- **Oxygen (O)** has an atomic number of 8.
- **Fluorine (F)** has an atomic number of 9.

As we move from nitrogen to fluorine, the atomic size decreases. Thus, fluorine is smaller than both nitrogen and oxygen.

### Step 4: Compare Fluorine with Fluoride Ion
Now we need to compare fluorine (F) with the fluoride ion (F⁻):
- Fluorine (F) has 9 electrons.
- Fluoride ion (F⁻) has 10 electrons.

### Step 5: Analyze the Effect of Additional Electron
When an extra electron is added to fluorine to form the fluoride ion (F⁻), the effective nuclear charge experienced by the outermost electrons decreases because there is one more electron than protons. This leads to a larger ionic radius for F⁻ compared to the neutral fluorine atom.

### Step 6: Conclusion
Since fluorine (F) has a smaller size than both nitrogen and oxygen, and the fluoride ion (F⁻) is larger than fluorine due to the additional electron, we conclude that:
- The smallest size among the given atoms and ions is that of **Fluorine (F)**.

### Final Answer
The atom with the smallest size is **Fluorine (F)**.

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