Final answer:
Most sodium reabsorption in the nephron occurs in the proximal convoluted tubule (PCT), which is equipped with cells that actively transport ions and have a high concentration of mitochondria to produce sufficient ATP.
Step-by-step explanation:
The question relates to the functioning of a nephron in the kidney, particularly where the reabsorption of sodium primarily occurs. Most of the reabsorption of sodium takes place in the proximal convoluted tubule (PCT). The PCT is responsible for the reabsorption and secretion of various solutes, including Na+, Cl−, and glucose. The cells in the PCT actively transport ions and possess numerous mitochondria to provide the necessary ATP for this activity. While other segments of the nephron, like the loop of Henle and the collecting ducts, also participate in reabsorption, the PCT is where the majority occurs.