Select correct answers from the choices A, B, C, D which are given. Write down only the letter corresponding to the correct answer.
A deep blue colour appears when excess of ammonium hydroxide is added to a solution containing the cation:
A I 3 + ; F e 2 + ; `Zn^(2+) ; `Cu^(2+) ;

Options

A. `AI^(3+)`
B. `Fe^(2+)`
C. `Zn^(2+)
D. `Cu^(2+)

Answer

To solve the question regarding which cation produces a deep blue color when excess ammonium hydroxide is added, we will analyze each option provided:

1. **Identify the cations**: The cations given are:
- A) \( \text{Al}^{3+} \)
- B) \( \text{Fe}^{2+} \)
- C) \( \text{Zn}^{2+} \)
- D) \( \text{Cu}^{2+} \)

2. **Understanding the reaction with ammonium hydroxide**:
- Ammonium hydroxide (\( \text{NH}_4\text{OH} \)) is a weak base that reacts with metal cations to form their respective hydroxides.

3. **Reactions with each cation**:
- **For \( \text{Al}^{3+} \)**:
- Forms \( \text{Al(OH)}_3 \) which is a gelatinous white precipitate.
- **For \( \text{Fe}^{2+} \)**:
- Forms \( \text{Fe(OH)}_2 \) which is a dirty green precipitate.
- **For \( \text{Zn}^{2+} \)**:
- Forms \( \text{Zn(OH)}_2 \) which is a white precipitate.
- **For \( \text{Cu}^{2+} \)**:
- Forms \( \text{Cu(OH)}_2 \) which is a pale blue precipitate.

4. **Effect of excess ammonium hydroxide**:
- When excess ammonium hydroxide is added to \( \text{Cu(OH)}_2 \), it forms a complex ion known as tetramine copper(II) complex, which is deep blue in color.

5. **Conclusion**:
- The cation that produces a deep blue color upon the addition of excess ammonium hydroxide is \( \text{Cu}^{2+} \).

Thus, the correct answer is **D**.

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