Deindividuation describes the phenomenon when an individual loses certain aspects of self-awareness within a group environment. Mostly commonly applied to situations of group violence or negative behaviors, deindividuation can arguably cause a group member to lose sense of his or her personal obligations, morals, and sense of responsibility. In this example, the young man describes getting "caught up" and "carried away" with the group while failing to consider his personal role in the events. Such a description would be considered characteristic of deindividuation.

The bystander effect refers to the inverse relationship between the number of people witnessing a negative event and the number of people that will assist in alleviating the negative outcome. As the young man described was a participant in the riot, rather than a bystander, we can eliminate this answer choice.

Social facilitation describes the likelihood for individuals to perform well on simple tasks when being watched by a group. Essentially, when one's talents are being evaluated by others, one tends to perform their existing talents better. This phenomenon is relatively unlinked to the situation described in the question.

Groupthink is a decision-making phenomenon driven by the desire for harmony within a group, and is used to justify irrational decisions and choices. A certain outcome may be reached solely to stabilize group loyalty and cohesion, rather than based on the consequences and effects of the outcome. While the situation described in the question outlines an instance of a group acting cohesively, the young man's response stems from a lack of cognitive awareness rather than a conscious desire to adhere to the group's actions.

Group polarization is another decision-making trend, and describes the tendency for group decisions to be more polarized toward given extremes than the viewpoints of the individual members. While the situation described certainly outlines a shift from moderate to extreme, there is again the issue of cognitive awareness and intention that allow us to eliminate this answer choice.

Deindividuation occurs when people are in a situation with a high degree of arousal and low feelings of responsibilities. In other words, it is a situation where individuals experience a loss of restraint and individual identity that is replaced with mob mentality. It can be described as a lack of self-awareness and results from disconnection of behavior from attitudes. Several factors create ideal conditions for deindividuation: group size, physical anonymity, and arousing activities.

Aggregates are groups of people who frequently exist in the same space but have little interactions. A person would be likely to experience deindividuation in this setting because of concepts like the bystander effect- people assume less responsibility because they believe someone else will take care of whatever issue is at hand, that someone else will do the right thing.

On the other hand, the other choices are incorrect. “Primary groups” are those close to you that you bond and interact heavily with; they serve expressive functions (i.e. where emotional needs are being met). We are closer and feel more generally responsible with these people. “Secondary groups” are usually task-oriented, impersonal, temporary, business-like relationships with instrumental purposes. We would be less likely to experience deindividuation with these groups because we would have a high feeling of responsibility for the tasks the group has been formed to tackle. “Counter-cultures” are distinct subcultures focused on stopping some dominant aspect of mainstream culture (like "anti-vaxxers"). Like an “out-group,” they are not a group with which someone would generally find common values, so they would be unlikely to induce deindividuation.