What is added to potassium ferrocyanide (Lassaigne nitrogen test) to give Prussian blue color?

Options

A. `FeCl_3`
B. `FeCl_2`
C. `CoCl_3`
D. `CoCl_2`

Answer

To solve the question regarding what is added to potassium ferrocyanide to give a Prussian blue color, we can follow these steps:

### Step 1: Understand the context of the question
The question pertains to the Lassaigne nitrogen test, which is used to detect the presence of nitrogen in organic compounds. Potassium ferrocyanide is a key reagent in this test.

**Hint:** Familiarize yourself with the Lassaigne test and its reagents.

### Step 2: Identify the chemical involved
Potassium ferrocyanide is represented by the formula K₄[Fe(CN)₆]. It contains iron (Fe) and cyanide (CN) ions.

**Hint:** Recall the composition of potassium ferrocyanide and its significance in the test.

### Step 3: Determine what is needed to produce the Prussian blue color
When potassium ferrocyanide is treated with ferric chloride (FeCl₃), a complex is formed that results in the characteristic Prussian blue color. The reaction can be summarized as follows:
\[ K_4[Fe(CN)_6] + 3 FeCl_3 \rightarrow Fe_3[Fe(CN)_6] + 3 KCl \]

**Hint:** Look for the specific iron compound that reacts with potassium ferrocyanide to produce the blue color.

### Step 4: Write the final answer
The substance that is added to potassium ferrocyanide to produce the Prussian blue color is ferric chloride (FeCl₃).

**Hint:** Confirm that you understand the role of FeCl₃ in the formation of the Prussian blue complex.

### Conclusion
The correct answer to the question is **ferric chloride (FeCl₃)**, which is option number 1.