Which of the following pairs of cations cannot be separate by using an NaOH solution?

Options

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

Answer

To determine which pairs of cations cannot be separated using an NaOH solution, we need to analyze the amphoteric nature of the cations involved. Amphoteric metals can react with both acids and bases, while non-amphoteric metals do not react with bases.

### Step-by-Step Solution:

1. **Identify the Cations**: The pairs of cations given in the question are:
- Option 1: Fe³⁺ and Al³⁺
- Option 2: Cr³⁺ and Al³⁺
- Option 3: Sn²⁺ and Pb²⁺
- Option 4: Cu²⁺ and Pb²⁺

2. **Determine Amphoteric Nature**:
- Amphoteric metals include: Zn, Al, Pb, Be, Sn, Sb, As, Ga, and Cr.
- Non-amphoteric metals include: Fe and Cu.

3. **Analyze Each Pair**:
- **Option 1 (Fe³⁺ and Al³⁺)**:
- Fe³⁺ is not amphoteric (does not react with NaOH).
- Al³⁺ is amphoteric (reacts with NaOH).
- **Conclusion**: They can be separated because one reacts and the other does not.

- **Option 2 (Cr³⁺ and Al³⁺)**:
- Both Cr³⁺ and Al³⁺ are amphoteric.
- **Conclusion**: They cannot be separated because both react with NaOH.

- **Option 3 (Sn²⁺ and Pb²⁺)**:
- Both Sn²⁺ and Pb²⁺ are amphoteric.
- **Conclusion**: They cannot be separated because both react with NaOH.

- **Option 4 (Cu²⁺ and Pb²⁺)**:
- Cu²⁺ is not amphoteric (does not react with NaOH).
- Pb²⁺ is amphoteric (reacts with NaOH).
- **Conclusion**: They can be separated because one reacts and the other does not.

4. **Final Answer**: The pairs of cations that cannot be separated using NaOH solution are:
- Option 2: Cr³⁺ and Al³⁺
- Option 3: Sn²⁺ and Pb²⁺

### Summary:
The pairs of cations that cannot be separated by using an NaOH solution are **Option 2 (Cr³⁺ and Al³⁺)** and **Option 3 (Sn²⁺ and Pb²⁺)**.