The second trophic level in an aquatic ecosystem is:

Zooplanktons

The correct answer is Option (4) - Zooplanktons

Explanation:

In an aquatic ecosystem, trophic levels are structured like this:

1. First Trophic Level – Phytoplanktons (autotrophic producers)
2. Second Trophic Level – Zooplanktons (primary consumers that feed on phytoplanktons)
3. Third Trophic Level – Small fishes (secondary consumers)
4. Fourth Trophic Level – Large fishes (tertiary consumers)