21.The maximum permissible limit for flouride in drinking water is 1.5 mg/litre
22.Standard EDTA (ethylene diamine terra acetic acid) solution is used to determine the hardness in water
23. If the coliform bacteria is present in a sample of water, then the coliform test to
be conducted is presumptive coliform test,confirmed coliform test,completed coliform test
24.Alkalinity in water is expressed as milligrams per litre in terms of equivalent
calcium carbonate
25.The product of H+ ions and OH- ions in a stronger alkali is
26.Which of the following values of pH represents a stronger acid? 2
27.Turbidity is measured on standard silica scale
28.On standard silica scale, the turbidity in drinking water should be limited to 10 ppm
29.Residual chlorine in water is determined by starch iodide method,orthotolidine method
30.Orthotolidine test is used for determination of residual chlorine
31.If the total hardness of water is greater than its total alkalinity, the carbonate
hardness will be equal to total alkalinity
32.The amount of residual chlorine left in public water supply for safety against
pathogenic bacteria is about 0.05 to 0.5 ppm
33.The dissolved oxygen level in natural unpolluted waters at normal temperature is found to be of the order of 10 mg/litre
34.The velocity of flow of water in a sedimentation tank is about 15 to 30 cm/minute
35.The length of rectangular sedimentation tank should not be more than 4B
where B is the width of the tank
36.The overflow rate for plain sedimentation tanks is about 500 to 750 litres/hour/m2
37.Percentage of bacterial load that can be removed from water by the process of
plain sedimentation is about 75
38.The settling velocity of a particle in a sedimentation tank depends on surface area of tank
39.The settling velocity of a particle in a sedimentation tank increases if none of the above
40.For a given discharge, the efficiency of sedimentation tank can be increased by
increasing the surface area of tank