Researchers conduct an experiment in which one group is exposed to treatment a and the other group is exposed to treatment b. if the group exposed to treatment a is designated as the treatment group, the group exposed to treatment b is the

The group exposed to Treatment B is the control group.

Explanation:

When conducting experiments, researchers use a control group and an experimental or treatment group. For the experimental group, the independent variable is exposed to changes, while in the control group it isn't. The results of both groups are then compared to measure the influence of the modified variable.

In this case, if the group called Treatment A is the one designated as the treatment group, the Treatment B group must be the control group.