Recommended level of residual chlorine for disinfection of water is:-
**Core Concept**
The recommended level of residual chlorine for disinfection of water is a critical parameter to ensure the effectiveness of water treatment processes and prevent waterborne diseases. The level of residual chlorine is measured in milligrams per liter (mg/L) and is typically expressed as free chlorine (HOCl) or combined chlorine (CLO2H+).
**Why the Correct Answer is Right**
The World Health Organization (WHO) recommends a minimum level of 0.5 mg/L of free chlorine for drinking water to ensure effective disinfection of pathogens. This level of chlorine is sufficient to inactivate bacteria, viruses, and protozoa that can cause waterborne diseases. The optimal level of residual chlorine also depends on factors such as water temperature, pH, and contact time. In general, a higher level of chlorine is required for colder water temperatures and shorter contact times.
**Why Each Wrong Option is Incorrect**
**Option A:** 0.1 mg/L is too low to effectively disinfect water, as it may not inactivate all pathogens, especially at higher water temperatures.
**Option B:** 1 mg/L may be excessive and can lead to the formation of harmful byproducts, such as trihalomethanes (THMs), which are known carcinogens.
**Option C:** No residual chlorine is not a viable option, as it would leave the water vulnerable to contamination.
**Clinical Pearl / High-Yield Fact**
It is essential to regularly test and maintain the optimal level of residual chlorine in water treatment systems to prevent waterborne diseases and ensure the safety of drinking water.
**Correct Answer: D. 1 mg/L**