Final answer:
The smallest biomass in the given food chain is likely to be at the level of the hawk, which is the apex predator and hence occupies the highest trophic level where energy and biomass are the least.
Step-by-step explanation:
In the food chain "grass → grasshopper → bird → hawk", the smallest biomass would typically be found at the highest trophic level, which in this chain is the hawk. This is because energy and biomass decrease with each successive trophic level in an ecological pyramid, due to factors such as energy loss through metabolic processes and heat. So the correct answer is B) hawk.
The food chain is a model that represents a single pathway through which energy flows in an ecosystem. Given that each level has fewer organisms that can be supported due to the less energy available, the apex predator, in this case, the hawk, typically has the least biomass.