Correct Answer - Option 2 : Nitrates
Explanation:
(i) Presence of nitrogen in water indicates presence of organic matter.
(ii) Presence of free ammonia in water indicates its recent pollution. Free ammonia should not be more than 0.15 mg/l.
(iii) The presence of organic ammonia indicates decomposition has just started and limiting value in potable water is 0.3 mg/l.
(iv) Among all form of nitrogen, nitrite is highly dangerous, hence its permissible limit is zero.
(v) Nitrate is not harmful becuase it is fully oxidised. Presence of nitrate in water is not harmful and it indicate complete decomposition of the organic matter but in some cases, if it present in excess it effect the infants resulting in the disease termed as mathemoglobinemia.
