Ecology involves the study of all of the following except for the interactions between
a. atoms.
b. individual organisms.
c. populations.
d. individual organisms and their environment.

A. atoms.
Ecology is the study of the organisms, the environment and their interaction. 
As living organisms in the biotic environment, human beings need food, water and resources in order to survive and thus, it is used in trading, buying and selling of the goods, where economics function. It also applies the supply and demand approach and uses strategy in how to maintain and innovate resources.