Option 1: Unerring -> means never making mistakes; this is a synonym of infallible, not an antonym.
Option 2: Flawed -> means having defects or imperfections; this is the opposite of infallible.
Option 3: Impeccable -> means without fault or error; this is a synonym of infallible, not an antonym.
Option 4: Explicable -> means able to be explained; this is unrelated to the concept of being error-free.
Hence, Option 2: Flawed -> "Infallible" means incapable of making mistakes or being wrong, while "flawed" means having defects or imperfections, making them perfect antonyms -> correct