Answer :
Ira's decision to cancel his canoe trip after hearing a weather forecaster warn of a severe thunderstorm passing through the area best illustrates the impact of normative social influence.
1. Normative social influence is when a person conforms to the expectations of others to gain approval or avoid disapproval. In this case, Ira may have canceled his trip to conform to the general belief that it's safer to avoid being out on the water during a severe storm. He might have been influenced by the social norm that prioritizes safety in such situations.
2. The other options, such as groupthink, social facilitation, and informational social influence, do not fit the scenario as well. Groupthink involves a group making decisions without critical evaluation, social facilitation is the tendency for people to perform better on simple tasks when in the presence of others, and informational social influence is when a person looks to others for guidance in an uncertain situation.
Therefore, in this context, Ira's decision aligns best with normative social influence, where he likely chose to cancel the trip to conform to social norms of safety during severe weather conditions.