An informal group is the one which has its own set of values, goals and leaders. Let the informal group be a group of friends and their goal is to attend a wedding. Them being not motivated to go to a wedding is a task for the group leader. Now, an expressive leader would use tools such as emotional and logical reasoning which would help the group to see why they should attend it. Whereas, an instrumental leader would recognize their needs and maybe offer an incentive which would allow the group to attend the wedding. In both ways, the leader achieves its output in terms of fulfilling the goal.
