Final answer:
The rats that were administered 0 ng/g BPA are the control group. They serve as a baseline for comparison, allowing any effects observed in treatment groups to be attributed to BPA exposure.
Step-by-step explanation:
Rats administered 0 ng/g BPA are considered the control group in the context of a scientific experiment. In any experimentation, control groups are essential as they receive an inactive treatment or placebo, ensuring they are managed in the same way as other groups which receive the treatment, except for the variable being tested. The purpose of a control group is to provide a baseline for comparison, allowing scientists to attribute any differences in outcomes to the variable being tested, in this case, BPA. For instance, the control group might receive no BPA while treatment groups receive varying doses of BPA; differences in response can then be linked to the presence or absence of this chemical.
In the given scenario, if the experiment aims to test the effects of BPA on some physiological aspect of the rats, then a group of rats not receiving BPA (0 ng/g) serves as control. This setup provides a reference to assess the impact of BPA treatment on other groups, helping to isolate the effects of BPA from other factors. Therefore, the 0 ng/g BPA group is not undergoing the treatment being tested (BPA exposure) and serves as the point of comparison for all other groups that are exposed to BPA.