Residual chlorine in drinking water should be-

Ans. is 'a' i.e., 0.5 mg /L Water typeRecommendedResidual chlorine levelContact periodDrinking water> 0.5 mg per litre (ppm)1 hourWater bodies, post disaster> 0.7 mg per litre (ppm)1 hourSwimming pool sanitation>1.0 mg per litre (ppm)1 hour