The organism that is a decomposer in the food web is bacterium.
OB. Bacterium
Analysis of the options
Snake (OA): Snakes are typically consumers and occupy a higher trophic level. They eat other animals but are not decomposers.
Bacterium (OB): Bacteria are decomposers. They play a crucial role in breaking down dead organic matter, such as dead plants or animals, into simpler substances.
Coyote (OC): Coyotes are consumers, specifically carnivores, and eat other animals. They are not decomposers.
Grass (OD): Grass is a producer and occupies the lowest trophic level. It undergoes photosynthesis to produce its own food and is not a decomposer.