Which word describes an atmosphere that is festive, sociable, and genial?

The word "convivial" is the most fitting choice to describe an atmosphere that is festive, sociable, and genial. This term derives from the Latin word "convivium," which refers to a gathering or feast characterized by friendly and lively interactions among participants. An atmosphere described as convivial implies warmth, cheerfulness, and a sense of community, where people enjoy each other's company and engage in enjoyable conversations and activities.

In contrast, the other options present different connotations. "Melancholic" relates to a deep sadness or sorrowful state, creating an atmosphere that is quite the opposite of festive. "Solemn" describes a serious, grave, or formal mood, which would not convey a sociable or genial environment. "Reserved" suggests a lack of warmth or openness, typically indicating a subdued or quiet demeanor that does not align with the idea of a friendly and celebratory atmosphere. Thus, "convivial" is the ideal word choice to encapsulate the essence of a lively and welcoming gathering.