What are the organisms called that physically and chemically break down complex dead organic remains?

Decomposers

The correct answer is Option (2)- decomposers.

Decomposers are organisms, such as bacteria and fungi, that break down complex dead organic matter into simpler substances through physical and chemical processes. This decomposition process recycles nutrients back into the ecosystem. Scavengers, on the other hand, consume dead organisms but do not typically break them down chemically as decomposers do.