Option 1: Talkative -> This is a synonym of loquacious, not an antonym.
Option 2: Garrulous -> This also means excessively talkative; it's a synonym, not opposite.
Option 3: Diligent -> This means hardworking and careful, which is unrelated to the concept of talkativeness.
Option 4: Taciturn -> This means reserved or saying little; it is the direct opposite of loquacious.
Hence, Option 4: Taciturn -> Loquacious means very talkative, while taciturn means reserved and uncommunicative in speech, making them perfect antonyms -> correct