Explanation:
Injunctive norms involve perceptions of which behaviors are usually approved or disapproved. They help an individual to understand what is acceptable and unacceptable social behavior.
Descriptive norms involve perceptions of which behaviors are typically performed. They normally refer to the perception of others' behavior, what people actually do and is based on our perception of the behavior of the people around us.
Brandon knows that society considers underage drinking to be wrong. His belief about most of the public would disapprove of underage drinking is Injunctive norms, while his perception under certain circumstances is Descriptive norms.