295. By adding 1 ml of orthotolidine solution to 100 ml chlorinated water taken after contact period, the residual chlorine makes the colour of solution
A. yellowish
B. greenish
C. bluish
D. reddish
296. Hardness of water can be removed by boiling if it is due to
A. calcium bicarbonates
B. calcium sulphates
C. calcium chloride
D. calcium nitrates.
297. One degree of hardness of water means a content of salts of
A. 10.25 mg/litre
B. 12.25 mg/litre
C. 14.25 mg/litre
D. 16.25 mg/litre.
298. The maximum permissible hardness for public supplies is
A. 95 mg/litre
B. 105 mg/litre
C. 115 mg/litre
D. 125 mg/litre
299. Permanent hardness of water can be removed by
A. adding alum
B. adding lime
C. adding chlorine
D. zeolite process.
300. Dissolved carbon dioxide, can be removed from the supply main by
A. sedimentation
B. aeration
C. chlorination
D. coagulation
301. To control the growth of algae in reservoirs, the compound which is used, is
A. bleaching powder
B. copper sulphate
C. lime solution
D. alum solution
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