Question

make an aquatic food chain up to territory consumer level.state the Tropic level at which concentration of pesticides is maximum and why?

Answer 1

(firstly, I believe its tertiary consumer, and trophic level)

A food chain can go as:
Phytoplankton (primary producers)⇒ Zooplankton (primary consumer) ⇒ Small fish (secondary consumer) ⇒ Large fish (sharks etc, tertiary consumer)

The role of pesticide comes in usually at the first level, since pesticides come in and generally have 2 effects on phytoplanktons:
a) They provide nutrients and cause immense increase in population, known     as Biomagnification.
b) They are harmful and kill the planktons

Answer 2

Aquatic food chain: Photoplanktons --> Zooplanktons --> Fish --> Shark

Pesticides are maximum at the tertiary level (here, shark). Chemicals get accumulated in larger amounts with an increase in trophic level. This is due to the phenomenon of Biomagnification.

Hope it helps...