Final answer:
Nephridia (Option 2)are the tube-shaped organs in mollusks that are responsible for nutrient reabsorption and waste excretion.
Step-by-step explanation:
In mollusks, the tube-shaped organs responsible for reabsorbing nutrients and excreting fluid waste are called nephridia. These structures are part of the excretory system and function to filter waste from body fluids. The nephridia release the filtered waste into the coelom and also have a system for tubular reabsorption. In contrast, a siphon is involved in the intake and expulsion of water, the radula is a feeding structure unique to mollusks, and the foot is typically used for movement or securement to surfaces.