In qualitative analysis, when `H_2S` is passed through an aqueous solution of salt acidified with dil.HCl, a black precipitate is obtained. On boiling the precipitate with dil. `HNO_3`, it forms a solution of blue colour. Addition of excess of aqueous solution of ammonia to this solution gives

Options

A. deep blue precipitate of `Cu(OH)_2`
B. deep blue solution of `[Cu(NH_3)_4]^(2+)`
C. deep blue solution of `Cu(NO_3)_2`
D. deep blue solution of `Cu(OH)_2.Cu(NO_3)_2`

Explanation

To solve the problem step by step, we will analyze the reactions and the compounds involved.

### Step 1: Passing H₂S through the acidified solution
When hydrogen sulfide (H₂S) is passed through an aqueous solution of a salt that is acidified with dilute hydrochloric acid (HCl), it reacts with certain metal ions present in the solution.

**Reaction:**
\[ \text{Cu}^{2+} + \text{H}_2\text{S} \rightarrow \text{CuS (s)} + 2\text{H}^+ \]

**Result:**
This reaction leads to the formation of a black precipitate of copper(II) sulfide (CuS).

### Step 2: Boiling the precipitate with dilute HNO₃
Next, when the black precipitate (CuS) is boiled with dilute nitric acid (HNO₃), it undergoes oxidation.

**Reaction:**
\[ \text{CuS} + 4\text{HNO}_3 \rightarrow \text{Cu(NO}_3)_2 + \text{H}_2\text{S} + 2\text{NO}_2 + 2\text{H}_2\text{O} \]

**Result:**
This reaction produces a blue solution of copper(II) nitrate (Cu(NO₃)₂).

### Step 3: Addition of excess aqueous ammonia
When excess aqueous ammonia (NH₃) is added to the blue solution of copper(II) nitrate, a complex ion is formed.

**Reaction:**
\[ \text{Cu(NO}_3)_2 + 4\text{NH}_3 \rightarrow \text{Cu(NH}_3)_4^{2+} + 2\text{NO}_3^- \]

**Result:**
This results in the formation of the tetraamminecopper(II) complex ion, \(\text{Cu(NH}_3)_4^{2+}\), which is deep blue in color.

### Conclusion
Thus, the final solution after the addition of excess ammonia is a deep blue solution of tetraamminecopper(II) ion.

### Final Answer
The addition of excess aqueous solution of ammonia to the blue solution gives a deep blue solution of \(\text{Cu(NH}_3)_4^{2+}\).

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