Answer:
a) Producers: grass, acorns
Primary consumers: squirrel, mouse, deer
Secondary consumers: coyote, cougar
Decomposers: mushrooms ( not a part of producers )
b) The organisms in first trophic level i.e. grass and acorns are going to have the highest population. They need to supply energy to the subsequent trophic levels. Since their biomass is less on individual level, their number needs to be high to be able to transfer enough energy to the next trophic level where the organisms have higher biomass.