<prompt> Ortho-toluidine test measures the levels of:Combined chlorineBoth free and combined chlorineNitrates in waterHardness of water  <response>: Ans. b. Both free and combined chlorineTest for chlorination of waterOrtho-toluidine test OTOrtho-toluidine Arsenite test OTA Free residual chlorine Free chlorine Free and Combined chlorine Combined chlorineOTA test is better than OT test as:Detects both free and combine water chlorine separately.Not affected by interfering substances Nitrites, Iron, and Manganese. 