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

Answer

To solve the question regarding the unknown salt 'A' that produces reddish-brown fumes when treated with potassium dichromate (K2Cr2O7) and concentrated sulfuric acid (H2SO4), we can follow these steps:

### Step 1: Understand the Reaction
When an unknown salt 'A' is treated with K2Cr2O7 and concentrated H2SO4, we need to identify the possible ions in salt 'A' that could lead to the formation of reddish-brown fumes. The two common ions that might be present are chloride ions (Cl-) and bromide ions (Br-).

### Step 2: Identify the Products of the Reaction
1. **If Salt 'A' contains Chloride ions (Cl-)**:
- The reaction will produce chromyl chloride (CrO2Cl2), which is known to release reddish-brown vapors.
- The reaction can be represented as:
\[ 2 K_2Cr_2O_7 + 14 H_2SO_4 + 6 Cl^- \rightarrow 6 CrO_2Cl_2 + 2 K_2SO_4 + 7 H_2O + 6 H_2SO_4 \]

2. **If Salt 'A' contains Bromide ions (Br-)**:
- The reaction will produce bromine (Br2), which also has reddish-brown vapors.
- The reaction can be represented as:
\[ 2 K_2Cr_2O_7 + 14 H_2SO_4 + 6 Br^- \rightarrow 6 Br_2 + 2 K_2SO_4 + 7 H_2O + 6 H_2SO_4 \]

### Step 3: Conclusion from the Observations
Both chloride and bromide ions produce reddish-brown fumes when reacted with K2Cr2O7 and H2SO4. Therefore, based on the observed reddish-brown fumes, we cannot definitively conclude whether chloride or bromide ions are present in salt 'A'.

### Step 4: Distinguishing Between Chloride and Bromide
To distinguish between the two ions:
- If the product (chromyl chloride) is treated with sodium hydroxide (NaOH), it will produce a yellow solution of sodium chromate (Na2CrO4), confirming the presence of chloride ions.
- If bromide ions are present, no such color change will occur upon treatment with NaOH.

### Final Conclusion
Since the reddish-brown fumes do not confirm the presence of either chloride or bromide ions without further testing (like treatment with NaOH), the correct statement regarding the observation is:
"It neither confirms the presence of chloride nor bromide unless it is passed through NaOH solution."