Correct option is A
heat flux from a fin’s surface is proportional to the local temperature difference between the fin surface and the ambient. For a typical fin the temperature falls from the base (root) toward the tip, so the largest local temperature (and therefore the largest local heat flux per unit area) occurs near the root. Placing more lateral surface area where the local driving temperature is greatest (near the root) yields more total heat transfer for a given fin volume or material.
