Which trophic level contains the organisms that are source of all chemical energy used in an ecosystem

The correct answer would be producers as they convert light energy to chemical energy by photosynthesis.

Explanation:

The food chain is a sequence of transfer of energy and food to one organism is consumed by the other.

Trophic level is the position or the place of organisms share in the food chain. Producers are the trophic level placed in the bottom of the food chain.

Producers (plants) convert light energy into chemical energy by the process of photosynthesis. This chemical energy transfer from one trophic level to another.  Producers provide food and energy to other trophic levels when they consume producer as their food. The green plants and blue-green algae are the examples of producer trophic level.

Thus, the correct answer would be producers.