**Disinfection of Water with Chlorine**

**Chlorine** is commonly used as a disinfectant in water treatment processes to kill or inactivate various types of pathogens, including bacteria, viruses, and protozoan parasites. It is a highly effective and widely used method for ensuring the safety of drinking water.

**Dosage of Chlorine for Disinfection**

The dosage of chlorine required for disinfection of water depends on multiple factors, including the quality of the water, the presence of pathogens, and the desired level of disinfection. The most common unit for measuring the dosage of chlorine is milligrams per liter (mg/L) of water.

The recommended dosage of chlorine for disinfection of water is about **1 mg/L**. This means that for every liter of water, a concentration of 1 milligram of chlorine is required for effective disinfection.

**Explanation of the Correct Answer**

The correct answer to the given question is option **D) 1 mg/L**. This dosage level is commonly recommended by various water treatment authorities and regulatory agencies for effective disinfection of water.

**Importance of Chlorine Dosage**

- **Pathogen Inactivation**: Chlorine at the recommended dosage of 1 mg/L is sufficient to kill or inactivate a wide range of pathogens, including bacteria, viruses, and protozoan parasites, present in the water. It helps to prevent waterborne diseases and ensures the safety of drinking water.

- **Residual Disinfection**: The dosage of 1 mg/L also ensures the presence of a residual disinfectant in the water. This residual chlorine can provide continuous disinfection and help to control the regrowth of pathogens in the distribution system.

- **Water Quality Considerations**: The dosage of chlorine may vary depending on the quality of the water being treated. For example, if the water contains a high level of organic matter or is heavily contaminated, a higher dosage of chlorine may be required to achieve effective disinfection.

- **Regulatory Standards**: The dosage of chlorine for disinfection of water is often regulated by national or international standards. These standards provide guidelines and limits for the acceptable levels of chlorine in drinking water to ensure its safety and quality.

It is important to note that the dosage of chlorine may vary for specific applications or circumstances. Therefore, it is recommended to refer to local regulations and guidelines or consult a water treatment professional for accurate dosage recommendations based on the specific water sources and treatment requirements.