Final answer:
The central idea of the text is that group dynamics significantly impact individual actions, encapsulated in the notion that a large group influences an individual's behavior.
Step-by-step explanation:
The central idea of the text focuses on how individuals' actions are influenced by group dynamics, which is best summarized by Option 1: The actions of a large group can greatly influence an individual's actions. The concept of deindividuation showcased in the text explains a reduction in personal accountability and sense of self when in a crowd, which can lead to behaviors like those in mobs or riots. Moreover, the emergent-norm theory indicates that crowds can develop their own norms, and the discussion of conformity and obedience under social influences further emphasizes the power of group dynamics on individual behavior. Collective behavior, mass behavior, and social control are other relevant concepts discussed, situating individuals' behavior within a larger social context.