Minimum contact period for chlorination -

Ans. is 'b' i.e., 1 hour Water typeRecommendedResidual chlorine levelContact periodDrinking waterWater bodies, post disasterSwimming pool sanitation> 0.5 mg per litre (ppm) >0.7 mg per litre (ppm)> 1.0 mg per litre (ppm)1 hour1 hour1 hour