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': "What is the reagent used in Horrock's apparatus for determining chlorine demand of water - \nSelect and explain. \nA. Ohotoluidine, B. Methylene blue, C. Stach iodide indicator, D. Sodium bicarbonate", 'role': 'user'}, {'content': "Answer: C \nExplanation: Horrock's apparatus is designed to find the dose of bleaching powder required for disjnfection of water. The indicator used is starch iodine indicator solution.Addition of the indicator to the cups with stock solution and water gives blue colour if there is free residual chlorine. Parks textbook of preventive and social medicine.K Park. Edition 23.Pg no: 729", 'role': 'assistant'}]