Which of the following aqueous solutions are acidic ?

Options

A. `CuSO_4`
B. `CH_3COONH_4`
C. `Na_2CO_3`
D. None of the above

Explanation

To determine which of the given aqueous solutions are acidic, we will analyze each option based on the nature of the compounds involved (whether they are acids, bases, or salts) and their respective pH values.

### Step-by-Step Solution:

1. **Identify the Compounds in Each Option:**
- **Option A:** Copper sulfate (CuSO₄)
- **Option B:** Ammonium acetate (CH₃COONH₄)
- **Option C:** Sodium bicarbonate (NaHCO₃)
- **Option D:** Sodium carbonate (Na₂CO₃)

2. **Analyze Option A: Copper Sulfate (CuSO₄):**
- Copper sulfate is a salt formed from the reaction of sulfuric acid (strong acid) and copper hydroxide (weak base).
- When dissolved in water, it can hydrolyze to produce H⁺ ions, leading to an increase in acidity.
- **Conclusion:** This solution is acidic.

3. **Analyze Option B: Ammonium Acetate (CH₃COONH₄):**
- Ammonium acetate is a salt formed from acetic acid (weak acid) and ammonia (weak base).
- The pH of this solution can be calculated using the formula:
\[ \text{pH} = \frac{1}{2}(\text{pK}_a + \text{pK}_b) \]
- Given that both pK values are equal (approximately 4.75), the pH will be around 7, indicating a neutral solution.
- **Conclusion:** This solution is neutral.

4. **Analyze Option C: Sodium Bicarbonate (NaHCO₃):**
- Sodium bicarbonate is a salt derived from a strong base (sodium hydroxide) and a weak acid (carbonic acid).
- The solution will have a pH greater than 7, indicating it is basic.
- **Conclusion:** This solution is basic.

5. **Analyze Option D: Sodium Carbonate (Na₂CO₃):**
- Sodium carbonate is also a salt formed from a strong base (sodium hydroxide) and a weak acid (carbonic acid).
- Similar to sodium bicarbonate, this solution will have a pH greater than 7, indicating it is basic.
- **Conclusion:** This solution is basic.

### Final Answer:
The only acidic solution among the options is **Option A: Copper sulfate (CuSO₄)**.

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