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
Indicator solution in Horrocks apparatus contains 
Select and explain. 
A. Oho toludine, B. Starch iodide, C. Ohotoludine arsenite, D. Bromocresol purple
B: Starch iodide
Answer: B: Starch iodide 
Explanation: Horrock&;s apparatus is designed to find out the dose of bleaching powder required for disinfection of water.Starch-iodide indicator solution is used.Park 23e pg: 728