Contaminated water can be purified by removing

Question

Accepted Answer

The correct answer is: **4. all of the above**

### Explanation:

Contaminated water can contain a variety of pollutants that need to be removed to make it safe for consumption and use. Let's analyze each option:

1. **Undesirable chemicals**: Contaminated water often contains harmful chemicals such as heavy metals (like lead and mercury), pesticides, and industrial pollutants. Removing these chemicals is crucial because they can pose serious health risks to humans and wildlife.

2. **Biological contaminants**: This includes bacteria, viruses, parasites, and other microorganisms that can cause diseases. Biological contaminants are a major concern in water quality, and their removal is essential for ensuring that water is safe to drink and use.

3. **Gases**: Water can also be contaminated with gases such as chlorine, methane, or hydrogen sulfide. These gases can affect the taste and odor of water and may also pose health risks. Removing these gases is important for improving water quality.

### Conclusion:

Since all of the listed contaminants—undesirable chemicals, biological contaminants, and gases—can be present in contaminated water, the correct approach to purifying water involves addressing all these issues. Therefore, the answer is **4. all of the above**, as effective water purification must encompass the removal of all types of contaminants to ensure safety and quality.