The colour of the solution/precipitate obtained in the elemental analysis of an organic compound and the molecule/ion responsible for the colour are given below. Choose the incorrectly matched pair:

Options

A. Prussian blue - `Fe_(4)[Fe(CN)_(6)]_(3).xH_(2)O`
B. Black - PbS
C. Violet colour - `[Fe(CN)_(5)NOS]^(4-)`
D. Yellow - `(NH_(4))_(2)MoO_(4)`

Explanation

To solve the question regarding the incorrectly matched pair of color and the corresponding molecule/ion in elemental analysis of organic compounds, we will analyze each option provided in the question step by step.

### Step 1: Analyze the first pair
- **Color**: Prussian blue
- **Molecule/Ion**: Na4[Fe(CN)6] (ferric ferrocyanide)

**Explanation**:
When nitrogen is present in an organic compound, it can be detected by fusing the compound with sodium to form NaCN. This is then reacted with iron(III) chloride (FeCl3) to produce Prussian blue, which is indeed correctly matched.

### Step 2: Analyze the second pair
- **Color**: Black
- **Molecule/Ion**: PbS (lead sulfide)

**Explanation**:
When sulfur is present in an organic compound, it is fused with sodium to form Na2S. When Na2S is reacted with lead acetate, it produces lead sulfide (PbS), which is a black precipitate. This is also correctly matched.

### Step 3: Analyze the third pair
- **Color**: Violet
- **Molecule/Ion**: Na4[Fe(CN)5NO]

**Explanation**:
When sulfur is present, it can also be detected using sodium nitroprusside, which gives a violet color when reacted with the sodium sulfide solution. This pair is correctly matched.

### Step 4: Analyze the fourth pair
- **Color**: Yellow
- **Molecule/Ion**: NH4[MoO4]

**Explanation**:
Phosphorus detection involves fusing the organic compound with sodium to form Na3PO4, which when treated with ammonium molybdate gives a yellow compound known as ammonium phosphomolybdate. However, the pair suggests NH4[MoO4], which is not the correct product for phosphorus detection. This is the incorrectly matched pair.

### Conclusion:
The incorrectly matched pair is the one with the yellow color and NH4[MoO4].

### Final Answer:
**Option D**: Yellow color with NH4[MoO4] is the incorrectly matched pair.

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