This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Body fluid compaments, Subject name: Physiology
5 g mannitol was injected intravenously. 40% of mannitol is excreted. After equilibrium, plasma concentration of mannitol is 30 mg%. Calculate extracellular fluid volume. 
Select and explain. 
A. 10 L, B. 14 L, C. 18 L, D. 24 L
A: 10 L
Answer: A: 10 L 
Explanation: The volume of water in different compament can be measured by volume of distribution principle (indicator dilution principle). Where v = Volume of fluid Q = Quantity of indicator given C = Concentration of the indicator e = The amount of indicator which has either been lost or metabolized 30 mg% = 30 mg/ 100 mL = 300 mg/ L = 0.3g/L Quantity of mannitol excreted = 5 * 40/100 = 2 g ECF volume = 5 - 2 / 0.3 = 3 / 0.3 = 10 L