Unknown salt `'A'+K_(2)Cr_(2)O_(7)+"conc. "H_(2)SO_(4) to `Reddish brown fumes. Which is the correct statement regarding the above observation?

Options

A. it confirms the presence of `Cl^(-)` ion
B. confirms the presence of `Br^(-)` ion
C. It confirms the presence of both
D. it neither confirms `Cl^(-)` nor `Br^(-)` unless it is passed through NaOH solution

Answer

To solve the question regarding the unknown salt 'A' reacting with potassium dichromate (K₂Cr₂O₇) and concentrated sulfuric acid (H₂SO₄) to produce reddish brown fumes, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reaction Components**:
The components involved in the reaction are the unknown salt 'A', potassium dichromate (K₂Cr₂O₇), and concentrated sulfuric acid (H₂SO₄).

2. **Understand the Nature of the Reaction**:
When potassium dichromate is mixed with concentrated sulfuric acid, it can act as an oxidizing agent. The unknown salt 'A' likely contains halide ions (like Cl⁻ or Br⁻) that can be oxidized.

3. **Possible Halide Ions**:
The unknown salt 'A' could contain either chloride ions (Cl⁻) or bromide ions (Br⁻). Both of these ions can react with potassium dichromate in the presence of concentrated sulfuric acid to produce reddish brown fumes.

4. **Formation of Reddish Brown Fumes**:
- If 'A' contains Cl⁻, the reaction will produce chromyl chloride (CrO₂Cl₂), which gives off reddish brown vapors.
- If 'A' contains Br⁻, the reaction will produce bromine gas (Br₂), which also appears as reddish brown vapors.

5. **Conclusion on the Observations**:
Since both reactions can produce reddish brown fumes, the observation alone does not confirm whether the unknown salt contains Cl⁻ or Br⁻.

6. **Confirmatory Test**:
To confirm the presence of either ion, the product can be treated with concentrated sodium hydroxide (NaOH).
- If chromyl chloride is formed, it will react with NaOH to produce sodium chromate (Na₂CrO₄), which is yellow in color.
- Bromine gas does not give a similar reaction with NaOH.

7. **Final Statement**:
Therefore, the correct statement regarding the observation of reddish brown fumes is that it does not confirm the presence of Cl⁻ or Br⁻ until further tests (like passing through NaOH) are conducted.