The reagents, `NH_(4)Cl` and aqueous `NH_(3)` will precipitate

Options

A. `Ca^(2+)`
B. `Al^(3+)`
C. `Mg^(2+)`
D. `Zn^(2+)`

Answer

To determine which ions will precipitate when reacting with Ammonium Chloride (NH₄Cl) and Aqueous Ammonia (NH₄OH), we can follow these steps:

### Step 1: Understand the Reaction
Ammonium Chloride (NH₄Cl) provides NH₄⁺ ions in solution, while Aqueous Ammonia (NH₄OH) provides OH⁻ ions. The combination of these ions can lead to the formation of hydroxides of certain metal ions.

### Step 2: Identify the Ions
The ions we are considering are:
- Calcium (Ca²⁺)
- Aluminium (Al³⁺)
- Magnesium (Mg²⁺)
- Zinc (Zn²⁺)

### Step 3: Analyze the Precipitation of Hydroxides
When NH₄⁺ and OH⁻ ions are present, they can react with the metal ions to form their respective hydroxides. We need to check which of these metal ions form insoluble hydroxides:

1. **Calcium Hydroxide (Ca(OH)₂)**: Soluble in water, does not precipitate.
2. **Aluminium Hydroxide (Al(OH)₃)**: Insoluble in water, will precipitate.
3. **Magnesium Hydroxide (Mg(OH)₂)**: Slightly soluble, but can precipitate under certain conditions.
4. **Zinc Hydroxide (Zn(OH)₂)**: Insoluble in water, will precipitate.

### Step 4: Conclusion
Among the given ions, Aluminium (Al³⁺) will definitely precipitate as Aluminium Hydroxide (Al(OH)₃). Magnesium (Mg²⁺) and Zinc (Zn²⁺) can also precipitate, but the question specifically asks for the ions that will precipitate with certainty. Therefore, the most definitive answer is Aluminium (Al³⁺).

### Final Answer
The reagents NH₄Cl and aqueous NH₃ will precipitate Aluminium ions (Al³⁺).

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