Answer:
Benthic zone.
Step-by-step explanation:
The aquatic ecosystem has been divided into the several zones according to the physical and biological environment of that zone. The zones of aquatic ecosystem are benthic, profundal, sediment and limnetic zone.
The benthic is the deepest zone of the aquatuc ecosystem. No light penetrates in this zone and plants are unable to live in this zone as their required light for their basic process.
Thus, the correct answer is option (3).