Option 1: Thrifty -> means economical and careful with money, which is the opposite of profligate.
Option 2: Restrained -> means showing self-control and moderation, which contradicts the meaning of profligate.
Option 3: Prompt -> means quick or on time, which is unrelated to the concept of profligate.
Option 4: Extravagant -> means recklessly wasteful or excessive in spending, which perfectly matches the meaning of profligate.
Hence, Option 4: Extravagant -> Profligate describes someone who is recklessly extravagant and wasteful with resources or money, making "extravagant" the correct synonym -> correct