Which one of the following salt solutions on reaction with excess of ammonium hydroxide solution gives a deep blue solution ?

Options

A. `FeCl_3(aq)`
B. `CuSO_4(aq)`
C. `Al_2(SO_4)_3(aq)`
D. `ZnSO_4(aq)`

Explanation

To solve the question regarding which salt solution reacts with excess ammonium hydroxide to give a deep blue solution, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Salts**: The question implies that we have several salt solutions to consider. Common salts that might be tested include copper sulfate (CuSO₄), iron(II) chloride (FeCl₂), zinc sulfate (ZnSO₄), and others.

2. **Understand the Reaction with Ammonium Hydroxide**: When a salt solution is mixed with ammonium hydroxide (NH₄OH), it can lead to the formation of a precipitate or a complex ion.

3. **Focus on Copper Sulfate**: Among the salts, copper sulfate (CuSO₄) is known to react with ammonium hydroxide. Initially, it forms a pale blue precipitate of copper hydroxide (Cu(OH)₂).

\[ \text{CuSO}_4 + 2 \text{NH}_4\text{OH} \rightarrow \text{Cu(OH)}_2 \downarrow + \text{(NH}_4)_2\text{SO}_4 \]

4. **Excess Ammonium Hydroxide**: When excess ammonium hydroxide is added, the copper hydroxide precipitate can further react to form a complex ion, specifically the tetraamminecopper(II) complex, which is deep blue in color.

\[ \text{Cu(OH)}_2 + 4 \text{NH}_4\text{OH} \rightarrow [\text{Cu(NH}_3)_4]^{2+} + 2 \text{OH}^- + 4 \text{H}_2\text{O} \]

5. **Conclusion**: The deep blue solution formed is due to the presence of the tetraamminecopper(II) complex. Therefore, the salt solution that gives a deep blue solution upon reaction with excess ammonium hydroxide is **copper sulfate (CuSO₄)**.

### Final Answer:
The salt solution that gives a deep blue solution when reacted with excess ammonium hydroxide is **copper sulfate (CuSO₄)**.