Option 1 -> Brave means courageous; it doesn't oppose the hostile/aggressive nature of belligerent.
Option 2 -> Friendly means peaceable and amiable, which is the direct opposite of belligerent (hostile/aggressive).
Option 3 -> Hostile is actually a synonym of belligerent, not an antonym.
Option 4 -> Bemused means confused or bewildered; it's unrelated to the concept of aggression.
Hence, Option 2: Friendly -> Belligerent describes someone who is hostile and eager to fight, while friendly describes someone who is peaceable and amiable, making them perfect antonyms -> correct