Social loafing is most likely to occur among a. audience members who are asked to applaud after a speaker is introduced b. factory workers paid on the basis of individual level of productivity c. a group of runners competing for first place in a race d. students who are each assigned a different topic for their course term papers

I believe the answer is: a.  audience members who are asked to applaud after a speaker is introduced.

Social loafing refers to the social process when an individuals start to making less effort to work when they're in a group setting compared to when they're working individually.
When audiences is asked to give applaud , most of you would notice that some of the audiences would clap slower or not clap at all because they believe the other audiences would cover for them.