Answer: c. deindividuation.
Step-by-step explanation:
In social psychology, deindividuation is a phenomenon of losing self-awareness when in a group. When under influence, it is easier for people to take certain action that they would not normally take when on their own. People feel less responsible for certain actions in a group, and believe that they are anonymous. As Mullen found in his research, members of a big group are capable of burning, lacerating and dismembering their victims.
Pluralistic ignorance is a situation in which members of a group privately disapprove of certain norms of a group, while they publicly support them.
Group polarization happens when group as a whole makes a decision that is more radical than what would have been decided by the members on their own.
Social loafing is a theory that people put less effort in a certain activity when they do it in a group than when they do it on their own.