Blindfolded people were observed to clap louder when they thought they were clapping alone than when they thought they were clapping with others. this best illustrates

I believe the answer is: Social loafing

Social loafing refers to the phenomenon when people decided to make less effort in achieving a certain goal if they're working in a group

They managed to do this because in a group setting, each members could cover each other's weakness and the individual effort that each members made would be accumulated by other's effort in driving the group toward a common goal.

Ibelieve appendix i maybe wrong