Which one of the following has the largest population in a food chain?

Decomposers. Producers. Primary consumers. Secondary consumers.

Decomposers.

Decomposers are the largest population of the food chain. The detritus food chain (DFC) begins with dead organic matter. It is made up of decomposers which are heterotrophic organisms, mainly fungi and bacteria. They meet their energy and nutrient requirements by degrading dead organic matter or detritus.