Option 1: Debase -> means to lower in quality or value, which is similar to vitiate, not opposite.
Option 2: Activate -> means to make active or effective, opposite of spoiling or impairing.
Option 3: Avenge -> means to take revenge, unrelated to vitiate.
Option 4: Offend -> means to cause displeasure or insult, not an antonym of vitiate.
Hence, Option 2: Activate -> Vitiate means to spoil, impair, or corrupt something, making it less effective. Activate means to make something active, functional, or effective, which is the direct opposite action -> correct