281. Pick up the correct statement from the following :
A. Lime may be used to soften the hard water
B. Excessive use of lime may kill the bacterias
C. Excessive lime when added to water, raises its pH value
D. All the above.

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282.  Pick up the incorrect statement from the following :
A. Water disinfected with ozone is free from any odour
B. Ozone removes bacterias as well as colour and odour
C. ozonised water becomes tasteless
D. None of these.

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283.  Disappearance of pink colour of water of a well due of KIIVIn04 indicates that water contains
A. acidity
B. alkalinity
C. turbidity
D. organic matter

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284. The pH value of water is kept slightly less than 7 so that hydrochloride ions may combine with ammonia ions to form
A. Mono-chloramine (NHC1)
B. Di-chloramine (NH2C1)
C. Nitrogen trichloramine (NC13)
D. All the above.

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285. The gaseous form of chlorine gets converted into liquid fbrm when subjected to a pressure of
A. 5 kg/cm2
B. 6 kg/cm2
C. 7 kg/cm2
D. 8 kg/cm2

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286.  The chlorine supply cylinders are generally kept at 38?C to 4000 to prevent
A. conversion into crystals
B. it from burning
C. it from explosion
D. none of these.

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287.  The duration of contact of chlorine with water before it is served to the first consumer, should be at least
A. 10 to 15 minutes
B. 15 to 20 minutes
C. 20 to 30 minutes
D. 30 to 40 minutes

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