Final answer:
In the study by Schachter and Singer, the informed group was immune to arousal manipulation because they were correctly informed about the effects of the epinephrine injection and thus did not misattribute their arousal to emotional changes.
Step-by-step explanation:
The group that was immune to the arousal manipulation in the initial study conducted by Schachter and Singer was the informed group. These participants received injections of epinephrine and were correctly informed about the physiological effects they should expect, such as symptoms of the fight-or-flight response. Since they were anticipating the physiological arousal, they did not attribute their feelings to a change in emotional state in response to the confederate's behavior, unlike the other groups who were not expecting these physiological changes.