Name the gas which is useful in water purification.

Options

A. Chlorine
B. Oxygen
C. Sulphur
D. Nitrogen

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the name of a gas that is useful in the process of water purification.

2. **Identifying the Need for Water Purification**: Water often contains impurities and harmful microorganisms, such as bacteria, which can pose health risks. Therefore, it is essential to purify water for safe consumption and use.

3. **Recognizing Common Water Purification Methods**: Various methods can be used for water purification, including filtration, boiling, and chemical treatment. Among these, chemical treatment is a common method that involves the use of gases.

4. **Identifying the Gas Used in Water Purification**: One of the most widely used gases for water purification is chlorine gas. Chlorine is known for its disinfectant properties, making it effective in killing bacteria and other pathogens present in water.

5. **Concluding the Answer**: Based on the above points, the gas that is useful in water purification is chlorine gas.

**Final Answer**: The gas which is useful in water purification is chlorine gas.

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