Option 1 -> Gullible means easily deceived or trusting, which relates to naivety rather than being the opposite of friendly.
Option 2 -> Surly means bad-tempered, unfriendly, and rude - the direct opposite of affable (friendly and pleasant).
Option 3 -> Tactless means lacking sensitivity or diplomacy, but doesn't directly oppose the friendly nature of affable.
Option 4 -> Gracious means courteous and kind, which is actually similar to affable, not opposite.
Hence, Option 2: surly -> Affable describes someone who is warm, friendly, and approachable, while surly describes someone who is bad-tempered, hostile, and unfriendly - making them perfect antonyms. -> correct