Neutral water with pH about 7 becomes slightly acidic when aerated this is because

Options

A. oxygen from air is dissolved in the water which makes the water acidic
B. dirt which get contaminated with the water during aeration makes the water acidic
C. ultraviolet radiation dissociates water molecules and makes water acidic
D. During aeration carbon dioxide present in air dissolves in neutral water having pH =7 and thus the water becomes slightly acidic due to the formation of weak carbonic acid `(H_(2)CO_(3))`

Explanation

To solve the question, "Neutral water with pH about 7 becomes slightly acidic when aerated. This is because...", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Neutral Water**:
- Neutral water has a pH of 7, which means the concentration of hydrogen ions (H⁺) and hydroxide ions (OH⁻) are equal.

2. **Aeration Process**:
- Aeration involves passing air through water. This process increases the contact between water and the gases present in the air.

3. **Presence of Carbon Dioxide (CO₂)**:
- Air contains various gases, including carbon dioxide (CO₂). When water is aerated, CO₂ from the air dissolves in the water.

4. **Formation of Carbonic Acid**:
- The dissolved CO₂ reacts with water (H₂O) to form carbonic acid (H₂CO₃):
\[ \text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{CO}_3 \]

5. **Dissociation of Carbonic Acid**:
- Carbonic acid is a weak acid and can dissociate in water to produce hydrogen ions (H⁺) and bicarbonate ions (HCO₃⁻):
\[ \text{H}_2\text{CO}_3 \rightleftharpoons \text{H}^+ + \text{HCO}_3^- \]

6. **Increase in Hydrogen Ion Concentration**:
- The dissociation of carbonic acid increases the concentration of H⁺ ions in the water. This leads to a situation where the concentration of H⁺ ions becomes greater than that of OH⁻ ions.

7. **Resulting pH Change**:
- Since pH is a measure of the concentration of H⁺ ions, an increase in H⁺ ions results in a decrease in pH, making the water slightly acidic (pH < 7).

8. **Conclusion**:
- Therefore, the correct explanation for why neutral water becomes slightly acidic when aerated is that carbon dioxide from the air dissolves in the water, forming carbonic acid which increases the concentration of H⁺ ions.

### Final Answer:
Neutral water with pH about 7 becomes slightly acidic when aerated because carbon dioxide present in the air dissolves in the water and forms carbonic acid, which increases the concentration of hydrogen ions (H⁺).

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