The correct option is **D. Cu(NH3)4(OH)2**. ### Step-by-Step Explanation: 1. **Understanding the Reaction**: - When copper(II) sulfate (CuSO4) solution is treated with ammonium hydroxide (NH4OH), a series of reactions occur. Initially, copper(II) hydroxide (Cu(OH)2) precipitates out of the solution. 2. **Formation of Precipitate**: - The reaction can be represented as: \[ \text{CuSO}_4 (aq) + 2 \text{NH}_4\text{OH} (aq) \rightarrow \text{Cu(OH)}_2 (s) + \text{(NH}_4)_2\text{SO}_4 (aq) \] - Here, Cu(OH)2 is formed as a blue precipitate. This precipitate is insoluble in water. 3. **Dissolution of Precipitate**: - When excess ammonium hydroxide is added, the precipitate of Cu(OH)2 dissolves. This occurs because the ammonia (NH3) in the solution forms a complex with the copper ions. - The reaction can be represented as: \[ \text{Cu(OH)}_2 (s) + 4 \text{NH}_3 (aq) \rightarrow \text{Cu(NH}_3)_4(OH)_2 (aq) \] - The resulting solution is deep blue due to the formation of the complex ion Cu(NH3)4(OH)2. 4. **Why Option D is Correct**: - The deep blue solution is specifically due to the presence of the tetraamminecopper(II) complex, Cu(NH3)4(OH)2. This complex is stable in solution and imparts the characteristic deep blue color. ### Analysis of Other Options: - **Option A: Cu(OH)2**: - While Cu(OH)2 is indeed formed initially as a precipitate, it does not remain in solution when excess NH4OH is added. Instead, it dissolves to form the complex, so this option is incorrect for the final solution. - **Option B: CuSO4·5H2O**: - This is the hydrated form of copper(II) sulfate, commonly known as blue vitriol. It is not formed in this reaction and does not represent the deep blue solution after the addition of excess ammonium hydroxide. Therefore, this option is incorrect. - **Option C: (NH4)2SO4**: - Ammonium sulfate is indeed produced in the reaction, but it does not contribute to the deep blue color of the solution. It is a byproduct and not the species responsible for the color change. Thus, this option is also incorrect. ### Common Pitfalls: - Students may confuse the initial precipitate Cu(OH)2 with the final solution. It is crucial to remember that the deep blue color is due to the complex formed after the precipitate dissolves. - Misunderstanding the role of ammonia in forming complexes can lead to incorrect conclusions about the final solution. ### Revision Summary: - The deep blue solution formed when excess ammonium hydroxide is added to copper(II) sulfate is Cu(NH3)4(OH)2. - Cu(OH)2 is the initial precipitate that dissolves in excess NH4OH. - Other options (Cu(OH)2, CuSO4·5H2O, and (NH4)2SO4) do not represent the final deep blue solution. - Understanding complex formation is key to solving similar problems in coordination chemistry.