The relationship between the number of organisms in the food chain and the size of the individual organisms within each level of the food chain is a) unpredictable. b) not proportional. c) directly proportional. d) inversely proportional. 28)

The relationship between the size of individual organisms and the number of organisms in a given trophic level is D) inversely proportional. 
This is because a larger organism must consume more in order to sustain itself. Therefore, there can either be more organisms of smaller size or less organisms with larger size, because the energy entering a given trophic level is limited.
This is also the basis of formation of biomass pyramids, the total mass at higher trophic levels decreases.