What does '$X$' represent in the given figure?

The highest $DDT$ concentration in an aquatic food chain shall occur in:

What does '$Z$' represent in the given figure?

The dental disease characterized by mottling of teeth due to the presence of a specific chemical in drinking water is caused by which of the following elements?

Which one of the following pesticides is banned now-a-days?

Biochemical Oxygen Demand $(BOD)$ may not be a good index for pollution for water bodies receiving effluents from