In ecological pyramid which one is absent

Ecological pyramids are graphic representations of the relationships between various trophic levels of an ecosystem in terms of number, biomass and energy.

There are certain limitations of ecological pyramids.
The ecological pyramids are constructed considering a simple food chain in the ecosystem. But in reality, an ecosystem comprises a complicated food web of multiple intermingled food chains. The existence of a food web stabilises the ecosystem as more food options are available to the organisms for survival.
Saprophytes (decomposers) are organisms that decompose the dead organic matter and thereby release the nutrients back into the environment. Despite playing such a vital role in the ecosystem, they are not given any place in ecological pyramids.

Hence, the correct option is C.