Answer: Social facilitation
Step-by-step explanation:
The social facilitation is one of the concept that helps in explain about the progress in the individual person's performance due to their good efforts and completing the given task more effectively due to the others presence.
The social facilitation is one of the type of concept that helps in explaining about the positive change in the performance of the people due to the social environment.
According to the given question, Alex cannot do workout more effectively alone at his home so he decided to go gym with his all friends and this given group or social behavior is basically result of the social facilitation.
Therefore, Social facilitation is the correct answer.