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 following atoms or ions has the smallest size, we can follow these steps:

### Step 1: Identify the Atoms/Ions
First, we need to identify the atoms or ions we are comparing. In this case, we are looking at nitrogen (N), oxygen (O), fluorine (F), and the fluoride ion (F⁻).

### Step 2: Understand the Periodic Trend
Next, we need to understand the periodic trend in atomic size. Atomic size generally decreases as you move from left to right across a period in the periodic table. This is due to the increase in effective nuclear charge, which pulls the electrons closer to the nucleus.

### Step 3: Compare the Sizes of N, O, and F
Since nitrogen, oxygen, and fluorine are all in the same period (Period 2), we can compare their sizes:
- Nitrogen (N) has the largest atomic size.
- Oxygen (O) is smaller than nitrogen but larger than fluorine.
- Fluorine (F) has the smallest atomic size among these three.

### Step 4: Consider the Fluoride Ion (F⁻)
Now, we need to consider the fluoride ion (F⁻). Anions are larger than their parent atoms because they have gained electrons. In the case of F⁻, it has one more electron than F, resulting in a total of 10 electrons and only 9 protons. This leads to a weaker attraction between the nucleus and the electrons, causing the size of the ion to increase.

### Step 5: Conclusion
From the comparison:
- Nitrogen (N) > Oxygen (O) > Fluorine (F) > Fluoride Ion (F⁻)
Thus, the smallest size among these is that of the fluorine atom (F).

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

---