This organism breaks down nonliving matter into energy-rich compounds giving it back to the soil is called a .

Decomposers

Explanation:

A decomposer breaks down complex organic material in nonliving matter into energy rich inorganic compounds which return to the soil. Decomposers are actually recyclers in nature. They recycle matter and return energy to the environment.

They are found at the last trophic level in every food chain. They are responsible for maintaining balance of materials in nature.

c) should be the answer.