Final answer:
Salman joined the group at work for the solidary benefit of experiencing belonging and social interaction, which aligns with options related to closeness or common goals.
Step-by-step explanation:
The reason why Salman joined the group at his new workplace is likely because of a solidary benefit, which is the satisfaction derived from the experience of working with other people who share similar interests and social needs. As the new employee felt lonely and subsequently found a group that shares jokes and interacts informally to alleviate work-related stress, the group provides a sense of belonging and social interaction which is vital to most people's well-being and can significantly improve job satisfaction. This aligns with options involving closeness or common goals from the given choices.