Minimum recommended concentration of free chlorine drinking water at the end of 1 hour is –
**Core Concept**
The World Health Organization (WHO) recommends a minimum concentration of free chlorine in drinking water to ensure its safety for human consumption. Free chlorine is a disinfectant that inactivates pathogens and microorganisms, thereby preventing waterborne diseases.
**Why the Correct Answer is Right**
The recommended concentration of free chlorine in drinking water is at least 0.5 mg/L (milligrams per liter) at the end of 30 minutes of contact time. This ensures that the water is disinfected effectively against a wide range of pathogens, including bacteria, viruses, and protozoa. The chlorine concentration is measured as free chlorine, which is the active form of chlorine that is available to inactivate pathogens.
**Why Each Wrong Option is Incorrect**
**Option A:** 0.2 mg/L is lower than the recommended concentration, which would not provide adequate disinfection against pathogens.
**Option B:** 0.8 mg/L is higher than the recommended concentration, which could potentially lead to unpleasant taste and odor in the water.
**Option C:** 1.0 mg/L is still higher than the recommended concentration and may cause eye irritation and other health issues.
**Clinical Pearl / High-Yield Fact**
It's essential to note that the recommended concentration of free chlorine in drinking water may vary depending on the presence of organic matter, temperature, and other factors. Regular monitoring of free chlorine levels is crucial to ensure the water remains safe for consumption.
**Correct Answer:** C. 0.5 mg/L.