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 regarding which mixture can be separated by concentrated sodium hydroxide (NaOH), we need to understand the properties of the oxides formed by different metal ions. Concentrated sodium hydroxide can separate amphoteric oxides from basic oxides.

### Step-by-Step Solution:

1. **Understand the Role of Sodium Hydroxide:**
Concentrated sodium hydroxide is a strong base that can react with certain metal oxides. It can dissolve amphoteric oxides and basic oxides, allowing for their separation.

2. **Identify Amphoteric and Basic Oxides:**
- **Amphoteric Oxides:** These oxides can react with both acids and bases. Examples include Al2O3 (aluminum oxide) and ZnO (zinc oxide).
- **Basic Oxides:** These oxides primarily react with acids. An example is Fe2O3 (iron(III) oxide).

3. **Evaluate the Options:**
We need to check each option for the presence of one amphoteric oxide and one basic oxide.
- **Option A:** Al3+ and Cr3+ both form amphoteric oxides (Al2O3 and Cr2O3). **Not a valid option.**
- **Option B:** Cr3+ (amphoteric oxide Cr2O3) and Fe3+ (basic oxide Fe2O3). **Valid option.**
- **Option C:** Al3+ (amphoteric oxide Al2O3) and Zn2+ (amphoteric oxide ZnO). **Not a valid option.**
- **Option D:** Zn2+ (amphoteric oxide ZnO) and Pb2+ (amphoteric oxide PbO). **Not a valid option.**

4. **Conclusion:**
The only valid option that contains one amphoteric oxide and one basic oxide is **Option B (Cr3+ and Fe3+)**.

### Final Answer:
Concentrated sodium hydroxide can separate a mixture of **Cr3+ and Fe3+**.

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