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Question

# How much bleaching powder (having 20% available chlorine) is needed to disinfect 10000 litres of water whose chlorine demand is 1.0 mg/l? It should be ensured that, after about 1 hour contact time 0.2 mg/l chlorine is available.

A
40 g
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B
30 g
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C
48 g
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D
68 g
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Solution

## The correct option is D 68 gTotal dosage of chlorine (mg/l) =Total demand (mg/l)+Residual (mg/l)Total dosage=(1+0.2)mg/l=1.2 mg/l For 10000 litre of water, chlorine required, =1000− l×1.2 mg/l=12000 mg=12 g This chlorine has to come from beaching powder which has 20% available chlorine Hence, Bleaching powder required =120.2g=60g Note: Since no answer is matching. We can take nearest as correct answer i.e., 68 g.

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