p-Amino-N,N-dimethylaniline is added to a strongly acidic solution of X. The resulting solution is treated with a few drops of aqueous solution of Y to yield blue colouration due to the formation of methylene blue. Treatment of aqueous solution of Y with reagent potassium hexacyanoferrate (II) leads to the formation of an intense blue precipitate. The precipitate dissolves on excess addition of the reagent. Similarly, the treatment of the solution of Y with the solution of potassium hexacyanoferrate (III) leads to a brown colouration due to the formation of Z.
Q. Compound Z is

Options

A. `Mg_2[Fe(CN)_6]`
B. `Fe[Fe(CN)_6]`
C. `Fe_4[Fe(CN)_6]_3`
D. `K_2Zn_3[Fe(CN)_6]_2`

Explanation

To solve the question, we need to analyze the reactions involving p-Amino-N,N-dimethylaniline, the acidic solution X, and the aqueous solution Y. Let's break it down step by step.

### Step 1: Identify the Reaction of p-Amino-N,N-dimethylaniline with Acidic Solution X
p-Amino-N,N-dimethylaniline is a basic compound that can react with a strongly acidic solution (let's assume this is an acid like HCl). When it is added to the acidic solution, it gets protonated, forming a salt. This protonation is essential for the subsequent reactions.

**Hint:** Consider how amines behave in acidic solutions and what products they form.

### Step 2: Formation of Methylene Blue
The resulting solution from Step 1 is treated with a few drops of aqueous solution Y. In the presence of sulfide ions (S²⁻), which can be present in solution Y, the protonated p-Amino-N,N-dimethylaniline can react to form methylene blue, which is a blue dye.

**Hint:** Think about the color changes and the compounds that can be formed from the reaction of amines with sulfide ions.

### Step 3: Reaction of Aqueous Solution Y with Potassium Hexacyanoferrate(II)
When the aqueous solution Y is treated with potassium hexacyanoferrate(II) (K4[Fe(CN)6]), it leads to the formation of an intense blue precipitate. This is due to the formation of a complex between the iron(II) ions and the cyanide ligands.

**Hint:** Recall the characteristic colors of complexes formed with hexacyanoferrate ions.

### Step 4: Dissolution of the Precipitate
The intense blue precipitate formed in Step 3 dissolves upon the addition of excess potassium hexacyanoferrate(II). This indicates that the complex formed is not stable in excess reagent, which is typical behavior for certain metal complexes.

**Hint:** Consider how the solubility of metal complexes can change with concentration and the presence of ligands.

### Step 5: Reaction of Solution Y with Potassium Hexacyanoferrate(III)
When the solution of Y is treated with potassium hexacyanoferrate(III) (K3[Fe(CN)6]), it leads to a brown coloration due to the formation of compound Z. This compound is likely a complex formed between iron(III) ions and cyanide ligands.

**Hint:** Identify the colors associated with different oxidation states of iron and their complexes.

### Conclusion: Identify Compound Z
Based on the reactions and the information provided, compound Z is likely to be potassium ferricyanide, which has the formula K3[Fe(CN)6]. This compound is known for its brown coloration.

### Final Answer
**Compound Z is K3[Fe(CN)6] (potassium ferricyanide).**