Final answer:
Chester I. Barnard's most significant contribution to management is his administrative theory, detailing the importance of communication, cooperation, and common purpose within organizations as social systems.
Step-by-step explanation:
The largest contribution of Chester I. Barnard to the study of management is associated with B) Administrative Theory, specifically through his seminal work, The Functions of the Executive where he introduced concepts of the formal organization, the acceptance theory of authority, and the functions of the executive within an administrative setting. His work emphasized the importance of cooperation among employees, the role of communication in management, and the necessity of a common purpose within an organization for its effectiveness and survival, which deviates from the mechanistic principles of Scientific Management espoused by Frederick Taylor and diverges from the findings of the Hawthorne Studies, which focused more on the psychological and social factors at work. Rather, Barnard saw organizations as complex Social Systems that required careful administrative strategies to function well.