26. Permanent hardness of water may be removed by the addition of

A. lime
B. soda ash
C. potassium permanganate
D. sodium bicarbonate

27. Both temporary and permanent hardness of water can be removed on boiling water with

A. calcium hydroxide
B. sodium carbonate
C. calcium oxide
D. calcium carbonate

28. Lagoons may be characterized as

A. anaerobic
B. facultative
C. aerated
D. all of these

29. Temporary hardness of water may be removed by adding

A. calcium hydroxide
B. calcium carbonate
C. calcium chloride
D. sodium bicarbonate

30. The maximum desirable limit (BIS of mercury in the drinking water is

A. 0.05 mg/l
B. 0.9 mg/l
C. 0.1 mg/l
D. 0.001 mg/l