In chlorination technique adopted for disinfecting the water, the minimum time of contact should be
- A5 min
- B20 minCorrect
- C60 min
- D120 min
Solution
Concept
Chlorine needs a minimum contact time with water to kill pathogens.
Step-by-step solution
1. Chlorine needs time to act on bacteria. 2. Textbooks give a minimum contact period of about 20 to 30 minutes. 3. Among the options, 20 min matches this. 4. So the answer is (B).
Explanation
After chlorine is added, it must stay in contact with the water long enough to kill bacteria. Standard MCQ books give 20 minutes as the minimum contact time. 30 minutes is commonly used in practice.
Why the other options are wrong
A: 5 min is too short for complete disinfection. C and D: 60 or 120 min are more than the minimum needed.
Shortcut
Chlorine contact time is about 20 to 30 min.
Common mistake
Choosing 60 min, thinking a longer time is the 'minimum'.
Correct answer: B) 20 min