Which of the following pairs of cations can be separted by using on adding NaOH solution?

Options

A. `Cu^(2+),Zn^(2+)`
B. `Pb^(2+),Al^(3+)`
C. `Sn^(2+),Pb^(2+)`
D. `Zn^(2+),Pb^(2+)`

Answer

To determine which pairs of cations can be separated by adding sodium hydroxide (NaOH) solution, we will analyze each pair based on their reactions with NaOH.

### Step-by-Step Solution:

1. **Identify the Cations in Each Pair:**
- Pair 1: Copper(II) (Cu²⁺) and Zinc(II) (Zn²⁺)
- Pair 2: Lead(II) (Pb²⁺) and Aluminum(III) (Al³⁺)
- Pair 3: Tin(II) (Sn²⁺) and Lead(II) (Pb²⁺)
- Pair 4: Zinc(II) (Zn²⁺) and Lead(II) (Pb²⁺)

2. **Analyze the Reaction of Each Cation with NaOH:**
- **Pair 1: Cu²⁺ and Zn²⁺**
- Cu²⁺ reacts with NaOH to form **Cu(OH)₂**, which is an insoluble blue precipitate.
- Zn²⁺ reacts with NaOH to form **Na₂[Zn(OH)₄]**, which is a soluble complex.
- **Conclusion:** Cu²⁺ can be separated from Zn²⁺ because Cu(OH)₂ precipitates out while Zn²⁺ remains in solution.

- **Pair 2: Pb²⁺ and Al³⁺**
- Pb²⁺ reacts with NaOH to form **Na₂[Pb(OH)₄]**, which is a soluble complex.
- Al³⁺ reacts with NaOH to form **Na₃[Al(OH)₆]**, which is also a soluble complex.
- **Conclusion:** Both Pb²⁺ and Al³⁺ are soluble in NaOH, so they cannot be separated.

- **Pair 3: Sn²⁺ and Pb²⁺**
- Sn²⁺ reacts with NaOH to form **Na₂[Sn(OH)₄]**, which is a soluble complex.
- Pb²⁺, as mentioned, forms a soluble complex with NaOH.
- **Conclusion:** Both Sn²⁺ and Pb²⁺ are soluble in NaOH, so they cannot be separated.

- **Pair 4: Zn²⁺ and Pb²⁺**
- Zn²⁺ forms a soluble complex with NaOH.
- Pb²⁺ also forms a soluble complex with NaOH.
- **Conclusion:** Both Zn²⁺ and Pb²⁺ are soluble in NaOH, so they cannot be separated.

3. **Final Conclusion:**
- The only pair of cations that can be separated by adding NaOH solution is **Copper(II) (Cu²⁺) and Zinc(II) (Zn²⁺)**.

### Answer:
The correct answer is **Copper(II) (Cu²⁺) and Zinc(II) (Zn²⁺)**.