`AI^(3+).Fe^3+. Cr^3+` are grouped together for qualitative analysis because their

Options

A. carbonates are insoluble in ammonia
B. hydroxides are insoluble in ammonia
C. sulphides are soluble in acids
D. electronic charge is the same

Answer

To answer the question of why \( \text{Al}^{3+}, \text{Fe}^{3+}, \text{Cr}^{3+} \) are grouped together for qualitative analysis, we can follow these steps:

### Step 1: Identify the Ions
We start by identifying the ions in question:
- Aluminum ion: \( \text{Al}^{3+} \)
- Iron ion: \( \text{Fe}^{3+} \)
- Chromium ion: \( \text{Cr}^{3+} \)

### Step 2: Understand the Grouping
These ions are grouped together in qualitative analysis because they share similar chemical properties, particularly in their behavior with hydroxides.

### Step 3: Hydroxide Formation
When these ions are treated with hydroxide ions (OH⁻), they form hydroxides:
- \( \text{Al(OH)}_3 \) (Aluminum hydroxide)
- \( \text{Fe(OH)}_3 \) (Iron(III) hydroxide)
- \( \text{Cr(OH)}_3 \) (Chromium(III) hydroxide)

### Step 4: Solubility in Ammonia
The key reason for their grouping is that the hydroxides of these ions are insoluble in ammonia (NH₄OH) and precipitate out of solution:
- \( \text{Al(OH)}_3 \), \( \text{Fe(OH)}_3 \), and \( \text{Cr(OH)}_3 \) are all insoluble in ammonia.

### Step 5: Group Reagents
In qualitative analysis, these ions are typically tested using group reagents. In this case, the group reagent is ammonium hydroxide (NH₄OH) in the presence of ammonium fluoride (NH₄F).

### Conclusion
Thus, \( \text{Al}^{3+}, \text{Fe}^{3+}, \text{Cr}^{3+} \) are grouped together for qualitative analysis because their hydroxides are insoluble in ammonia, leading to their precipitation as hydroxides.

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