Final answer:
Paul would likely use the blocking skill to protect Anna from the negative reactions of the group by preventing further harmful interactions.
Step-by-step explanation:
In the scenario where Anna's behavior is causing a negative reaction in a counseling group, and given that she is relatively vulnerable to the group's reaction, the most appropriate group leadership skill Paul would likely utilize is blocking. Blocking is a skill used to protect group members from harmful or counterproductive interactions. By intervening in the situation, Paul can prevent the conversation from escalating and causing emotional harm to Anna or further disruption in the group. It would involve stepping in to stop the negative comments and refocusing the group's attention on constructive communication patterns.