<prompt> In water testing from a well containing 75000 litres of water by Horrocks apparatus, there is blue color from 4th cup onwards. What is the amount of bleaching powder required to disinfect the water -1000 gm1300 gm1600 gm2000 gm  <response>: Ans. is b i.e., 1300 gm o In Horrocks 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 ono 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---4551318gms 