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
Which of teh following is not true regarding bleaching powder- 
Select and explain. 
A. Contact period is one hour, B. Volume of water is estimated, C. Immediately dissolved in water, D. Chlorine demand is estimated
C: Immediately dissolved in water
Answer: C: Immediately dissolved in water 
Explanation: CHEMICAL DISINFECTION (1) Bleaching powder: Bleaching powder or chlorinated lime (Ca0Cl2 ) is a white amorphous powder with a pungent smell of chlorine. When freshly made, it contains about 33 per cent of "available chlorine". It is, however, an unstable compound. On exposure to air, light and moisture, it rapidly loses its chlorine content. But when mixed with excess of lime, it retains its strength; this is called "stabilized bleach." Bleaching powder should be stored in a dark, cool, dry place in a closed container that is resistant to corrosion. The chlorine content of bleaching powder stocks should be frequently checked. The principle in chlorination is to ensure a "free" residual chlorine of 0.5 mg/litre at the end of one hour contact. Highly polluted and turbid waters are not suited for direct chlorination Ref: Park 25th edition Pgno : 753