In water testing from a well (containing 75000 litres of water) by Horrock's apparatus, there is blue color from 4th cup onwards. What is the amount of bleaching powder required to disinfect the water -

Ans. is 'b' i.e., 1300 gm o In Horrock's apparatus, 6 cups are filled with water and indicator (starch iodine) is added in increasing quantity in each cup (1 unit in 1 st, 2 units in 2nd, 3 units in third and so on)o The first cup which shows the blue color is multiplied by 2, for example if 2nd cup shows blue colour than 4 grams (2x2) of bleaching powder will required to disinfect 455 litre of water,o In this question, 4th cup is showing blue color. So, 8 gms (4x2) of bleaching powder is required to disinfect 455 litre of water. Thus, total water of well require -Amount of bleaching powder =8x75000------455=1318gms