Correct Answer: C. excess nitrates
Solution:The disease, popularly called blue baby disease, or technically as methaemoglobinemia, is caused in children by the presence of excess nitrates in water. Fortunately, however, when the child grows, say above 6 months or so, the chances of conversion of nitrate into nitrite gets meagre due to development of the child's intestinal tract, and hence such a disease does not normally occur afterwards.