As group size increased, individual effort decreased, this phenomenon is called as:

Correct option is B

Social loafing refers to the tendency for individuals to exert less effort when working in groups compared to working alone. As group size increases, individual accountability decreases, leading to reduced effort. Ringelmann's rope-pulling experiments first demonstrated this: individuals pulled harder alone than in groups. This occurs because individual contributions become less identifiable in larger groups.

Information Booster:
• First demonstrated by Ringelmann (1913) in rope-pulling tasks
• Occurs when individual contributions are not identifiable
• Related to diffusion of responsibility
• Reduced in cultures with collectivist values
• Can be minimized by making individual contributions identifiable
• Opposite of social facilitation (improved performance when observed)

Additional Knowledge:
• Option (A) Social categorization: Process of classifying people into groups
• Option (C) Social exclusion: Being left out or rejected from groups
• Option (D) Social comparison: Evaluating oneself by comparing to others