Which of the following is halogen exchange reaction ?

Options

A. `RX+NaI rarr RI + NaX`
B.
C. `R-OH+HX overset(ZnCl_(2))rarr R-X+H_(2)O`
D.

Answer

To determine which of the given reactions is a halogen exchange reaction, we first need to understand what a halogen exchange reaction entails.

### Step-by-Step Solution:

1. **Definition of Halogen Exchange Reaction**:
A halogen exchange reaction occurs when one halogen atom in a compound is replaced by another halogen atom. This typically involves a nucleophilic substitution reaction where a halide ion (X-) from one compound replaces a halide ion in another compound.

2. **General Reaction Format**:
The general format for a halogen exchange reaction can be represented as:
\[ R-X_1 + NaX_2 \rightarrow R-X_2 + NaX_1 \]
Here, \( R \) is an organic group, \( X_1 \) and \( X_2 \) are different halogens, and \( Na \) is a sodium ion.

3. **Analyzing the Options**:
We will analyze the given options to identify which one represents a halogen exchange reaction.

- **Option A**: \( R-X + NaI \) → \( R-I + NaX \)
- In this reaction, a halogen (X) is replaced by iodine (I). This fits the definition of a halogen exchange reaction.

- **Option B**: (Addition Reaction)
- This does not involve any halogen exchange, as it does not include halides.

- **Option C**: (Alcohol Reaction)
- This option involves alcohols, which do not contain halogens. Therefore, it cannot be a halogen exchange reaction.

- **Option D**: (Toluene Reaction)
- Toluene does not contain halogens either, and the reaction does not involve any halogen exchange.

4. **Conclusion**:
Based on the analysis, the only option that represents a halogen exchange reaction is **Option A**.

### Final Answer:
The correct option for the halogen exchange reaction is **A**.