Residual chlorine in chlorination of water should be-
**Core Concept**
Chlorination of water is a disinfection process used to eliminate pathogenic microorganisms. Residual chlorine refers to the amount of chlorine that remains in the water after the initial disinfection process. The goal of residual chlorine is to maintain a sufficient concentration to prevent re-growth of microorganisms.
**Why the Correct Answer is Right**
The correct answer is 0.5 mg/L. The World Health Organization (WHO) recommends a residual chlorine concentration of 0.5 mg/L to ensure that the water remains safe for consumption. This concentration is sufficient to inactivate most bacteria, viruses, and protozoa, while also being safe for human consumption. The presence of residual chlorine also serves as an indicator of the effectiveness of the disinfection process.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a residual chlorine concentration of 1 mg/L is higher than the recommended level, which can lead to unpleasant taste and odor in the water, as well as potential health risks.
**Option B:** This option is incorrect because a residual chlorine concentration of 0.1 mg/L is lower than the recommended level, which may not be sufficient to prevent the re-growth of microorganisms.
**Option C:** This option is incorrect because a residual chlorine concentration of 1.5 mg/L is higher than the recommended level, which can lead to health risks and unpleasant taste and odor in the water.
**Clinical Pearl / High-Yield Fact**
It's essential to note that the optimal residual chlorine concentration can vary depending on factors such as water temperature, pH, and the presence of organic matter.
**Correct Answer:** 0.5 mg/L