Ohotolidine test is used to determine ?

Ans. is 'c' i.e., Free and combined chlorine in water Ohotolidine test (OT test) It is used to determine both free and combined chlorine in water with speed and accuracy. In this test. the reagent (0 tolidine, dissolved in 10% solution of HCL) is dissolved in tml of water containing o chlorine. The water turns yellow and the intensity of the colour varies with the concentration of the gas. The yellow colour is produced by both free and combined chlorine residuals. o Ohotolidine instantaneously reacts with free chlorine. %n h i le it react more slowly with combined chlorine. o Time taken to produce colour Free chlorine within seconds (10s) Combined chlorine 15-20 minutes