Answer:
exist primarily for the benefit of their members.
Step-by-step explanation:
Informal groups in an organization are created when individuals form a bond based on the experience that they share, they appear from friendship and not by rules inside the company but they influence how people interact and how they perform their job. Also, companies promote the apperance of these groups because they help people interact and improve their communication. According to that, the answer is that informal groups exist primarily for the benefit of their members as they are created by the friendship between employees and not by the company.
The other options are not right because informal groups don't perform routine organizational goals or uncommon tasks of the organization, they don't have a high level of interdependence and they are not initiated by the organization for special purposes because they are created by the employees and are not part of the company's structure.