The correct answer is social loafing.
Social loafing refers to the phenomenon in which individuals are more likely put in less effort and "slack off" when it comes to tasks if they are in a group compared to when they are working on a task alone. Social loafing likely occurs because in group work, each member pools together their skills and knowledge, therefore, no single person is required to put in the same amounts of efforts as they would if they were working alone.