Final answer:
The rapid infusion of 2 litres of normal saline leads to increased extracellular fluid volume, with no change in intracellular fluid volume or sodium concentration in the ECF.
Step-by-step explanation:
The correct answer to the question Rapid infusion of 2 litres of normal saline causes is D. Increased ECF, unchanged ICF, unchanged [Na+]. When 2 litres of normal saline, which is isotonic with the blood plasma, are infused rapidly into the body, the extracellular fluid (ECF) volume will increase. Since normal saline has a similar concentration of sodium and chloride ions as the ECF, there will be no net movement of water into or out of the cells; thus, the intracellular fluid (ICF) volume will remain unchanged. Sodium concentration ([Na+]) in the ECF will also remain unchanged, as the infused solution has the same concentration as the ECF.