Final answer:
Informal groups among the options provided are Friendship and Interest groups. These groups generally lack formal hierarchy and are built on personal connections or shared pastimes.
Step-by-step explanation:
Groups within a social context can be classified as either formal or informal based on their structure and purpose. Among the options provided, the groups classified as informal are Friendship and Interest groups (C). Friendship groups are often informal as they are comprised of people who bond over shared personal connections rather than structured roles. They generally involve face-to-face interactions in long-term emotional ways, serving emotional needs. Interest groups, like those formed around hobbies or volunteer activities, might have shared objectives but often lack a formal hierarchy, making them informal as well.
Examples of formal groups include task and command groups, where there are clear roles, responsibilities, and a chain of command, often found in workplaces or classrooms. Virtual and functional groups can be either formal or informal depending on their specific purpose and structure.