This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
[{'content': 'Break point chlorination means: \nSelect and explain. \nA. Start of chlorination process, B. End of chlorination process, C. When free residual chlorine starts appearing, D. After partial saturation of water with chlorine', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The addition of chlorine to water to a point at which free residual chlorine begins to appear is called breakpoint chlorination.\nThe "chlorine demand" of the water should be estimated. The chlorine demand of the water is the difference between the amount of chlorine added to the water and the amount of residual chlorine remaining at the end of a specific period of contact at a given temperature and pH of the water.\nThe point at which the chlorine demand of the water is met is called the "breakpoint". If further chlorine is added beyond the breakpoint, free chlorine begins to appear in the water.\n\nEssentials of preventive and community dentistry\nSoben Peter\n5th edition\nPage number 466', 'role': 'assistant'}]