This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and Health, Subject name: Social & Preventive Medicine
[{'content': 'Ortho-toluidine test measures the levels of: \nSelect and explain. \nA. Combined chlorine, B. Both free and combined chlorine, C. Nitrates in water, D. Hardness of water', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. b. Both free and combined chlorineTest for chlorination of waterOrtho-toluidine test (OT)Ortho-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).', 'role': 'assistant'}]