Option 1: Affordable -> means inexpensive or reasonably priced; unrelated to temperament or mood.
Option 2: Irritable -> means easily annoyed or angered; this is actually a synonym of irascible, not an antonym.
Option 3: Refutable -> means capable of being disproven; unrelated to personality traits or temperament.
Option 4: Amiable -> means friendly, pleasant, and good-natured; this is the direct opposite of irascible (quick-tempered).
Hence, Option 4: Amiable -> Irascible describes someone who is easily angered or hot-tempered, while amiable describes someone who is friendly and pleasant-natured, making them perfect antonyms -> correct