Halogens exist in `-1, +1, +3, +5 and +7` oxidation states. The halogen that exists only `-1` state is

Options

A. `Cl`
B. `I`
C. `F`
D. `Br`

Answer

To solve the question, we need to identify which halogen exists only in the -1 oxidation state.

### Step-by-Step Solution:

1. **Understanding Halogens and Their Oxidation States**:
- Halogens are a group of elements in Group 17 of the periodic table, which include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
- They can exhibit various oxidation states: -1, +1, +3, +5, and +7.

2. **Analyzing the Oxidation States**:
- The -1 oxidation state is typical for halogens when they gain one electron to achieve a stable electronic configuration.
- Other oxidation states (+1, +3, +5, +7) occur when halogens can lose electrons or share them.

3. **Identifying the Halogens**:
- **Fluorine (F)**: Atomic number 9, electronic configuration: 1s² 2s² 2p⁵. Fluorine is the most electronegative element and does not have d-orbitals, meaning it cannot expand its octet. Therefore, it can only exist in the -1 oxidation state.
- **Chlorine (Cl)**: Atomic number 17, electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁵. Chlorine can exist in multiple oxidation states, including +1, +3, +5, and +7.
- **Bromine (Br)**: Atomic number 35, electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁵. Bromine can also exhibit multiple oxidation states.
- **Iodine (I)**: Atomic number 53, electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁵. Iodine can also have multiple oxidation states.

4. **Conclusion**:
- Among the halogens, only fluorine exists solely in the -1 oxidation state due to its high electronegativity and lack of d-orbitals.

### Final Answer:
The halogen that exists only in the -1 oxidation state is **Fluorine (F)**.

---