Which of the following mixtures cann be separated by using excess `NH_(3) ` solution?

Options

A. `Bi^(3+)(aq.) ane Al^(3+)(aq.)`
B. `Al^(3+)(aq.) and Zn^(2+)(aq.)`
C. `Hg^(2+)(aq.) and Pb^(2+)(aq.)`
D. `Cu^(2+)(aq.) and Cd^(2+)(aq.)`

Explanation

To determine which of the following mixtures can be separated using excess ammonia solution, we will analyze each pair of ions and their behavior when treated with ammonia.

### Step-by-Step Solution:

1. **Identify the Ions in Each Mixture:**
- Mixture A: \( \text{Bi}^{3+} \) and \( \text{Al}^{3+} \)
- Mixture B: \( \text{Al}^{3+} \) and \( \text{Zn}^{2+} \)
- Mixture C: \( \text{Hg}^{2+} \) and \( \text{Pb}^{2+} \)
- Mixture D: \( \text{Cu}^{2+} \) and \( \text{Cd}^{2+} \)

2. **Analyze Mixture A (\( \text{Bi}^{3+} \) and \( \text{Al}^{3+} \)):**
- When ammonia is added, both \( \text{Bi(OH)}_3 \) and \( \text{Al(OH)}_3 \) precipitate out as white solids.
- In excess ammonia, neither precipitate dissolves. Therefore, they cannot be separated.

3. **Analyze Mixture B (\( \text{Al}^{3+} \) and \( \text{Zn}^{2+} \)):**
- Ammonia leads to the formation of \( \text{Al(OH)}_3 \) (gelatinous white precipitate) and \( \text{Zn(OH)}_2 \) (white precipitate).
- In excess ammonia, \( \text{Zn(OH)}_2 \) dissolves to form a colorless solution of \( \text{[Zn(NH}_3\text{)}_4]^{2+} \), while \( \text{Al(OH)}_3 \) remains as a precipitate.
- Thus, they can be separated by filtration.

4. **Analyze Mixture C (\( \text{Hg}^{2+} \) and \( \text{Pb}^{2+} \)):**
- Ammonia leads to the formation of \( \text{Hg}_2\text{Cl}_2 \) (white precipitate) and \( \text{Pb(OH)}_2 \) (also a white precipitate).
- In excess ammonia, neither precipitate dissolves. Therefore, they cannot be separated.

5. **Analyze Mixture D (\( \text{Cu}^{2+} \) and \( \text{Cd}^{2+} \)):**
- Ammonia leads to the formation of \( \text{Cu(OH)}_2 \) (blue precipitate) and \( \text{Cd(OH)}_2 \) (white precipitate).
- In excess ammonia, both \( \text{Cu(OH)}_2 \) and \( \text{Cd(OH)}_2 \) dissolve to form soluble complexes \( \text{[Cu(NH}_3\text{)}_4]^{2+} \) and \( \text{[Cd(NH}_3\text{)}_4]^{2+} \).
- Thus, they cannot be separated.

### Conclusion:
The only mixture that can be separated using excess ammonia solution is **Mixture B: \( \text{Al}^{3+} \) and \( \text{Zn}^{2+} \)**.

### Final Answer:
**The correct answer is Mixture B: \( \text{Al}^{3+} \) and \( \text{Zn}^{2+} \).**

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