Final answer:
The Hawthorne studies concluded that social relations among workers and the psychological perceptions of being observed, known as the Hawthorne effect, had a greater impact on productivity than the physical work environment.
Step-by-step explanation:
One of the conclusions from the Hawthorne studies was that social relations among workers have a greater effect on productivity than physical environment, which corresponds to option (b) groups can sometimes restrict the productivity of their members. The Hawthorne studies, conducted by Elton Mayo and his colleagues at Western Electric's Hawthorne Works, initially aimed to understand the impact of physical work conditions on productivity. However, they uncovered a phenomenon known as the Hawthorne effect: the change in behavior of individuals who are aware they are being observed by researchers or supervisors, which leads to increased performance. This effect highlighted the importance of psychological and social factors in the workplace over the modification of physical factors like lighting levels or break times.