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: Social & Preventive Medicine
Estimation of free chlorine of water is done by: March 2012, March 2013 (c, g) 
Select and explain. 
A. Ohotolidine test, B. Horrock's apparatus, C. Paterson's chloronome, D. Kata thermometer
A: Ohotolidine test
Answer: A: Ohotolidine test 
Explanation: Ans: A i.e. Ohotolidine test Test/instruments and their use Ohotolidine test enables both free and combined chlorine in water to be determined with speed and accuracy Horrock's water testing apparatus is designed to find out the dose of bleaching powder required for disinfection of water Paterson's chloronome is one such device for measuring, regulating and administering gaseous chlorine to water supplies Kata thermometer was originally devised for measuring the "cooling power" of the air. The Kata thermometer is now largely used as an anemometer for recording low air velocities rather than the cooling power of the air