Final answer:
The easiest and fastest search task, according to the feature positive effect, is searching for an item with a unique, distinctive feature. Informational social influence is more likely when the answer is unclear and the group has expertise. Option c) is correct.
Step-by-step explanation:
Based on what we know about the feature positive effect, we should predict that searching for an item with a unique, distinctive feature should be the easiest and fastest task. This is because the feature positive effect refers to the tendency of people to more easily notice and process stimuli that have distinctive features as opposed to stimuli without such features or those that share features with other items in the environment.
Regarding informational social influence, it will be more likely under conditions where the answer is unclear and when the group has expertise. These are situations where individuals look to the group for guidance and are more likely to conform to the group's opinion when they believe the group is more knowledgeable or where the correct course of action is ambiguous.