Which two gases should be present in potable water?

Options

A. Oxygen and carbon dioxide
B. Oxygen and nitrogen dioxide
C. Carbon dioxide and sulphur dioxide
D. Sulphur dioxide and nitrogen dioxide

Explanation

To determine which two gases should be present in potable water, we need to analyze the options given and understand the implications of each gas in water.

### Step-by-Step Solution:

1. **Understanding Potable Water**:
- Potable water is defined as water that is safe for drinking. It should not contain harmful chemicals or pollutants.

2. **Evaluating the Options**:
- **Option A: Oxygen and Carbon Dioxide**:
- Both of these gases are soluble in water. Oxygen is essential for aquatic life and is also beneficial for human health when dissolved in water. Carbon Dioxide is naturally present in water and is not harmful in small amounts.
- **Option B: Oxygen and Nitrogen Dioxide**:
- While oxygen is beneficial, Nitrogen Dioxide is harmful. When it combines with water, it forms Nitric Acid, which is corrosive and can damage tissues.
- **Option C: Carbon Dioxide and Sulphur Dioxide**:
- Carbon Dioxide is generally safe, but Sulphur Dioxide is a pollutant. It can react with water to form Sulphuric Acid, which is harmful.
- **Option D: Sulphur Dioxide and Nitrogen Dioxide**:
- Both gases are harmful. Sulphur Dioxide can form Sulphuric Acid, and Nitrogen Dioxide can form Nitric Acid, both of which are dangerous.

3. **Conclusion**:
- The only option that includes gases that are safe and beneficial in potable water is **Option A: Oxygen and Carbon Dioxide**.

### Final Answer:
The two gases that should be present in potable water are **Oxygen and Carbon Dioxide**.

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