Option 1: Confused -> This is an antonym; perspicacious means having clear understanding, not being confused.
Option 2: Insightful -> This correctly captures the meaning of perspicacious, which refers to having keen mental perception and understanding.
Option 3: Forgetful -> This relates to memory, not mental acuity or understanding.
Option 4: Naive -> This suggests inexperience and lack of sophistication, opposite to the sharp discernment that perspicacious implies.
Hence, Option 2: Insightful -> Perspicacious describes someone with acute mental vision and understanding, making "insightful" the perfect synonym -> correct