### Correct Option: A. A blue precipitate is formed which is soluble in excess ammonia. #### Detailed Explanation: When aqueous ammonia (NH₃) is added to a solution containing copper(II) ions (Cu²⁺), a series of reactions occur that lead to the formation of a specific precipitate and its subsequent behavior in the presence of excess ammonia. 1. **Initial Reaction**: - Copper(II) ions in solution are typically blue due to the presence of hydrated copper(II) ions, represented as [Cu(H₂O)₆]²⁺. - When you add aqueous ammonia dropwise to this solution, it reacts with the copper(II) ions to form a precipitate of copper(II) hydroxide, Cu(OH)₂. The reaction can be represented as: \[ \text{Cu}^{2+} (aq) + 2 \text{NH}_3 (aq) + 2 \text{H}_2\text{O} (l) \rightarrow \text{Cu(OH)}_2 (s) + 2 \text{NH}_4^+ (aq) \] - The precipitate of copper(II) hydroxide is a light blue solid. 2. **Observation of Precipitate**: - The initial addition of ammonia results in the formation of a blue precipitate (Cu(OH)₂). This is the first observable change when ammonia is added. 3. **Excess Ammonia**: - When more ammonia is added (in excess), the blue precipitate of copper(II) hydroxide dissolves to form a complex ion, specifically the tetraamminecopper(II) complex, [Cu(NH₃)₄]²⁺. The reaction can be represented as: \[ \text{Cu(OH)}_2 (s) + 4 \text{NH}_3 (aq) \rightarrow [\text{Cu(NH}_3)_4]^{2+} (aq) + 2 \text{OH}^- (aq) \] - This complex ion is also blue in color, but it is now soluble in the solution. #### Why Other Options Are Incorrect: - **Option B: Brick red precipitate is produced which is insoluble in excess ammonia**: - This option is incorrect because a brick red precipitate is characteristic of copper(I) oxide (Cu₂O), which does not form in this reaction. Copper(II) hydroxide is the relevant precipitate, and it is blue, not brick red. Additionally, Cu(OH)₂ is soluble in excess ammonia, contrary to what this option states. - **Option C: White precipitate is formed which is insoluble in excess ammonia**: - This option is incorrect because the precipitate formed is not white; it is blue (Cu(OH)₂). Furthermore, Cu(OH)₂ is soluble in excess ammonia, which contradicts the claim of being insoluble. - **Option D: Green precipitate is formed which is insoluble in excess ammonia**: - This option is incorrect as well. A green precipitate is not formed in this reaction. The only precipitate formed is blue (Cu(OH)₂), and it is soluble in excess ammonia, not insoluble. ### Summary of Key Points: - Aqueous ammonia reacts with copper(II) ions to form a blue precipitate of copper(II) hydroxide (Cu(OH)₂). - The blue precipitate dissolves in excess ammonia to form the soluble complex [Cu(NH₃)₄]²⁺. - The initial precipitate is blue, not brick red, white, or green, and it is soluble in excess ammonia. - Understanding the behavior of metal hydroxides in the presence of ligands like ammonia is crucial for predicting the outcomes of such reactions.