In drinking water, the amount of free ammonia should not exceed
- A0.15 mg/lCorrect
- B0.30 mg/l
- C0.50 mg/l
- D1.00 mg/l
Solution
Concept
Free ammonia in water shows recent organic (sewage) pollution. In drinking water it should not exceed 0.15 mg/l.
Step-by-step solution
1. Free ammonia indicates fresh decomposition of organic matter. 2. The textbook limit for free ammonia in potable water is 0.15 mg/l. 3. The limit for albuminoid ammonia is 0.3 mg/l. 4. So the answer is 0.15 mg/l, which is option A.
Explanation
Free ammonia comes from recent pollution by organic matter. Even a small amount is a warning sign, so the limit is very low: 0.15 mg/l.
Why the other options are wrong
B (0.30 mg/l) is the limit for albuminoid ammonia, not free ammonia. C and D are too high.
Shortcut
Free ammonia 0.15, albuminoid ammonia 0.30 (albuminoid is double).
Common mistake
Mixing up the free ammonia limit (0.15) with the albuminoid ammonia limit (0.30).
Correct answer: A) 0.15 mg/l