Which of the following anion has the smallest radius?

Options

A. `H^(-)`
B. `F^(-)`
C. `Cl^(-)`
D. `Br^(-)`

Answer

To determine which anion has the smallest radius among the given options (hydrogen ion, fluorine ion, chlorine ion, and bromine ion), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Anions**: The anions we are comparing are:
- Hydrogen ion (H⁻)
- Fluoride ion (F⁻)
- Chloride ion (Cl⁻)
- Bromide ion (Br⁻)

2. **Understand Periodic Trends**:
- Anions are negatively charged ions formed when an atom gains electrons.
- The size of anions generally increases as you move down a group in the periodic table due to the addition of electron shells.
- Conversely, as you move from left to right across a period, the size of the anions decreases due to increased nuclear charge, which pulls the electrons closer to the nucleus.

3. **Compare the Anions**:
- **Hydrogen Ion (H⁻)**: Located in the first period, it has only one electron shell.
- **Fluoride Ion (F⁻)**: Located in the second period, it has two electron shells.
- **Chloride Ion (Cl⁻)**: Located in the third period, it has three electron shells.
- **Bromide Ion (Br⁻)**: Located in the fourth period, it has four electron shells.

4. **Analyze Size Trends**:
- As we move down the group from fluorine to chlorine to bromine, the size of the anions increases. Therefore, Br⁻ > Cl⁻ > F⁻.
- Between H⁻ and F⁻, F⁻ is larger because it has more protons and electrons, which leads to a greater effective nuclear charge compared to H⁻.

5. **Conclusion**:
- Comparing all the anions, we find that the fluoride ion (F⁻) has the smallest radius among the given options.
- Thus, the answer is **Fluoride ion (F⁻)**.

### Final Answer:
The anion with the smallest radius is the **Fluoride ion (F⁻)**.