Concentrated sodium hydroxiide can separate a mixture of:

Options

A. `Al^(3+) and Cr^(3+)`
B. `Cr^(3+) and Fe^(3+)`
C. `Al^(3+) and Zn^(2+)`
D. `Zn^(2+) and Pb^(2+)`

Explanation

To solve the question about which mixture can be separated by concentrated sodium hydroxide (NaOH), we need to analyze the properties of the metal cations involved and their corresponding oxides. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Metal Cations and Their Oxides
We have four pairs of metal cations:
1. Aluminium (Al³⁺) and Chromium (Cr³⁺)
2. Chromium (Cr³⁺) and Iron (Fe³⁺)
3. Aluminium (Al³⁺) and Zinc (Zn²⁺)
4. Zinc (Zn²⁺) and Lead (Pb²⁺)

Next, we need to identify the oxides formed by these metal cations:
- Al³⁺ forms Al₂O₃ (amphoteric oxide)
- Cr³⁺ forms Cr₂O₃ (amphoteric oxide)
- Fe³⁺ forms Fe₂O₃ (basic oxide)
- Zn²⁺ forms ZnO (amphoteric oxide)
- Pb²⁺ forms PbO (amphoteric oxide)

### Step 2: Classify the Oxides
From the above, we classify the oxides:
- Amphoteric oxides: Al₂O₃, Cr₂O₃, ZnO, PbO
- Basic oxide: Fe₂O₃

### Step 3: Determine the Mixture that Can Be Separated
Concentrated sodium hydroxide can separate a mixture when one metal cation forms an amphoteric oxide and the other forms a basic oxide.

Now we analyze each pair:
1. **Al³⁺ and Cr³⁺**: Both form amphoteric oxides (Al₂O₃ and Cr₂O₃).
2. **Cr³⁺ and Fe³⁺**: Cr₂O₃ is amphoteric, and Fe₂O₃ is basic.
3. **Al³⁺ and Zn²⁺**: Both form amphoteric oxides (Al₂O₃ and ZnO).
4. **Zn²⁺ and Pb²⁺**: Both form amphoteric oxides (ZnO and PbO).

### Step 4: Conclusion
The only mixture where one metal cation forms an amphoteric oxide and the other forms a basic oxide is the second pair: Chromium (Cr³⁺) and Iron (Fe³⁺). Therefore, concentrated sodium hydroxide can separate this mixture.

### Final Answer
Concentrated sodium hydroxide can separate a mixture of **Chromium (Cr³⁺) and Iron (Fe³⁺)**.

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