Option 1 -> Sociable means friendly and outgoing, which relates to social behavior, not energy levels.
Option 2 -> Vivacious means lively, animated, and full of energy - the direct opposite of enervated.
Option 3 -> Languid means lacking energy or sluggish - this is actually a synonym of enervated, not an antonym.
Option 4 -> Decadent means characterized by moral or cultural decline, or excessive indulgence - unrelated to energy levels.
Hence, Option 2: Vivacious -> "Enervated" means weakened or drained of energy, while "vivacious" means full of life and energy, making them perfect antonyms -> correct