Which of the following can be prepared only by electrolysis 

Options

A. `Cl_2`
B. `Br_2`
C. `F_2`
D. `I_2`

Answer

To determine which of the following elements can be prepared only by electrolysis, we need to analyze each option: chlorine, bromine, fluorine, and iodine.

### Step-by-Step Solution:

1. **Understanding Electrolysis**:
Electrolysis is a chemical process that uses electrical energy to drive a non-spontaneous reaction. It is often used to decompose compounds into their constituent elements.

2. **Analyzing Each Element**:
- **Chlorine (Cl2)**: Chlorine can be prepared through the electrolysis of sodium chloride (NaCl) solution (brine). However, it can also be produced through other chemical reactions, such as the reaction of hydrochloric acid with manganese dioxide. Therefore, chlorine is not prepared exclusively by electrolysis.

- **Bromine (Br2)**: Bromine can be obtained from its compounds through various chemical reactions, including oxidation of bromide salts. Thus, bromine is not limited to electrolysis for its preparation.

- **Fluorine (F2)**: Fluorine is highly reactive and a strong oxidizing agent. It cannot be prepared by simple chemical reactions due to its reactivity. The only feasible method to produce fluorine gas is through the electrolysis of potassium fluoride (KF) or other fluoride salts. Therefore, fluorine can only be prepared by electrolysis.

- **Iodine (I2)**: Iodine can be extracted from iodide salts through oxidation reactions, such as reacting iodide with chlorine or other oxidizing agents. Hence, iodine is not exclusively prepared by electrolysis.

3. **Conclusion**:
Based on the analysis, the element that can be prepared only by electrolysis is **Fluorine (F2)**.

### Final Answer:
**Fluorine (F2)** can be prepared only by electrolysis.