Final answer:
Among at-risk youth undergoing brain scans, those with abnormalities in brain structure are considered to be most at risk of engaging in violent behavior.
Step-by-step explanation:
In the context of Sam, a psychologist who conducts brain scans of at-risk youth, those most at risk of engaging in violent behavior are likely to be individuals with abnormalities in brain structure. This is because research suggests that structural brain abnormalities can be associated with psychiatric disorders and behavioral issues. Additionally, studies indicate an association between aggressive behavior and altered serotonergic function, implying that adolescents with lower levels of serotonin may also be more prone to violent behavior. However, between the provided choices, option C, those with abnormalities in brain structure, would be considered most at risk according to current scientific understanding.