Option 1 -> Eternal means lasting forever or permanently, which is the opposite of ephemeral.
Option 2 -> Transient means lasting for a short time, which is actually a synonym of ephemeral, not an antonym.
Option 3 -> Indifferent means showing no interest or concern, which is unrelated to the concept of duration.
Option 4 -> Insightful means having deep understanding or perception, which is unrelated to the concept of duration.
Hence, Option 1: Eternal -> Ephemeral means short-lived or temporary, so its antonym must convey permanence or infinite duration, which eternal perfectly captures -> correct