Salt A `overset("Layer test") to` If reddish brown layer come first , then

Options

A. `Br^(Θ)` present
B. `Br^(Θ)` absent
C. `Cl^(Θ)` present
D. `I^(Θ)` present

Explanation

To solve the problem regarding the layers test for salt A, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Layers Test**:
- The layers test is a qualitative analysis method used to detect halide ions (specifically bromide and iodide ions) in a salt mixture.

2. **Observation of the Test**:
- When salt A is subjected to the layers test, a reddish-brown layer appears first. This indicates the presence of certain ions.

3. **Reagents Used**:
- Chlorine water is used in the test. When bromide ions (Br⁻) are treated with chlorine water, they undergo a reaction.

4. **Chemical Reaction**:
- The reaction can be represented as follows:
\[ 2 \text{Br}^- + \text{Cl}_2 \rightarrow 2 \text{Cl}^- + \text{Br}_2 \]
- In this reaction, bromide ions are oxidized to bromine (Br₂), which is reddish-brown in color.

5. **Layer Formation**:
- The bromine (Br₂) that is formed dissolves in the organic layer (like carbon tetrachloride, CCl₄), resulting in the reddish-brown color observed.

6. **Absence of Iodide Ions**:
- Iodide ions (I⁻) are oxidized preferentially compared to bromide ions. Therefore, if a reddish-brown layer is observed, it indicates that iodide ions are absent in the sample.

7. **Conclusion**:
- Since the reddish-brown layer is formed due to the presence of bromide ions and the absence of iodide ions, we conclude that bromide ions are present in salt A.

### Final Answer:
- The ion present in salt A is **bromide ion (Br⁻)**.