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

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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.

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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.

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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

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299.  Permanent hardness of water can be removed by
A. adding alum
B. adding lime
C. adding chlorine
D. zeolite process.

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300. Dissolved carbon dioxide, can be removed from the supply main by
A. sedimentation
B. aeration
C. chlorination
D. coagulation

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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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