`Sr^(2+)` can be precipitated by

Options

A. `(NH_4)_2 SO_4`
B. `NH_4CI`
C. `(NH_4)_2C_2O_4`
D. Both (A) and (C)

Answer

To determine how \( \text{Sr}^{2+} \) (strontium ions) can be precipitated, we need to analyze the possible reagents that can react with strontium ions to form insoluble compounds.

### Step-by-Step Solution:

1. **Identify Possible Precipitants**:
Strontium ions can precipitate with certain anions to form insoluble salts. Common precipitating agents for strontium include sulfate ions and oxalate ions.

2. **Precipitation with Sulfate**:
- When strontium ions react with sulfate ions, they form strontium sulfate (\( \text{SrSO}_4 \)), which is insoluble in water.
- The reaction can be represented as:
\[ \text{Sr}^{2+} + \text{SO}_4^{2-} \rightarrow \text{SrSO}_4 \downarrow \]
- Here, the downward arrow indicates the formation of a precipitate.

3. **Precipitation with Oxalate**:
- Strontium ions can also react with oxalate ions to form strontium oxalate (\( \text{SrC}_2\text{O}_4 \)), which is also insoluble in water.
- The reaction can be represented as:
\[ \text{Sr}^{2+} + \text{C}_2\text{O}_4^{2-} \rightarrow \text{SrC}_2\text{O}_4 \downarrow \]

4. **Exclusion of Ammonium Chloride**:
- Ammonium chloride (\( \text{NH}_4\text{Cl} \)) does not provide any precipitating anions that can form an insoluble compound with strontium ions.
- Therefore, it cannot be used to precipitate \( \text{Sr}^{2+} \).

5. **Conclusion**:
- From the above reactions, we conclude that strontium ions can be precipitated by both sulfate ions and oxalate ions.
- Thus, the correct answer is that \( \text{Sr}^{2+} \) can be precipitated by both options A (sulfate) and C (oxalate).

### Final Answer:
Strontium ions (\( \text{Sr}^{2+} \)) can be precipitated by sulfate ions and oxalate ions, making the correct option D (both A and C).