In which of the following case a violet colouration be observed?

Options

A. An alkaline solutino of sodium nitroprusside is treated with a solution of `Na_(2)S`
B. A solution of sodium cobaltinitrite is treated with one of KCl
C. A solution of `Mn(NO_(3))_(2)` is treated with sodium bismuthate or red lead in the presence of concentrated `HNO_(3)`
D. A solution of sodium nitroprusside in aqueous NaOH is treated with `Na_(2)SO_3`

Answer

To determine in which case a violet coloration is observed, we will analyze each option step by step.

### Step 1: Analyze Option A
**Reaction**: An alkaline solution of sodium nitroprusside (Na2[Fe(CN)5NO]) is treated with sodium sulfide (Na2S).

- **Reaction**: Na2[Fe(CN)5NO] + Na2S → Na4[Fe(CN)5NOS] (violet complex)
- **Observation**: The resulting complex is violet in color.

**Conclusion**: Violet coloration is observed in this case.

### Step 2: Analyze Option B
**Reaction**: A solution of sodium cobalt nitrite (Na3[Co(NO2)6]) is treated with potassium chloride (KCl).

- **Reaction**: Na3[Co(NO2)6] + KCl → K3[Co(NO2)6] (yellow precipitate) + NaCl
- **Observation**: The precipitate formed is yellow, not violet.

**Conclusion**: No violet coloration is observed in this case.

### Step 3: Analyze Option C
**Reaction**: A solution of manganese(II) nitrate (Mn(NO3)2) is treated with sodium bismuthate (NaBiO3) in the presence of concentrated HNO3.

- **Reaction**: Mn(NO3)2 + NaBiO3 + HNO3 → 2 HMnO4 (violet) + by-products
- **Observation**: The product HMnO4 is violet in color.

**Conclusion**: Violet coloration is observed in this case.

### Step 4: Analyze Option D
**Reaction**: A solution of sodium nitroprusside is treated with sodium sulfite (Na2SO3).

- **Reaction**: Na2[Fe(CN)5NO] + Na2SO3 → No violet complex formed
- **Observation**: This reaction is specifically a test for sulfide ions and does not yield a violet coloration.

**Conclusion**: No violet coloration is observed in this case.

### Final Conclusion
The violet coloration is observed in:
- Option A: Alkaline solution of sodium nitroprusside treated with Na2S.
- Option C: Solution of Mn(NO3)2 treated with NaBiO3 in the presence of concentrated HNO3.