What is the fourth stage of group development where group members form a cohesive relationship called?

The correct stage in the context of group development that represents the formation of a cohesive relationship among group members is Collaboration. In this phase, team members develop a strong sense of unity and begin to work together effectively towards shared goals. They establish trust and open communication, allowing for the exploration of diverse ideas, constructive feedback, and mutual support.

Collaboration is critical, as it signifies a transition from initial conflict or uncertainty to a well-functioning team dynamic. Members become more committed to team objectives, actively participate in discussions, and leverage each other's strengths.

The other stages mentioned, such as Adjourning, which relates to the disbanding of the group after achieving its goals, or Orientation, which refers to the initial phase where members are getting to know each other and establishing roles, do not focus on this development of cohesive relationships in the same way. Differentiation, while important in some contexts, typically refers to the process in which group members begin to specialize in their roles and may become more independent, which doesn't directly encompass the cohesive relationship aspect as described in the question.