This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Pharmacology
At equilibrium the concentrations of Cl- inside and outside a cell are 8 mmol/L and 120 mmol/L, respectively. The equilibrium potential for Cl- at 37oC is calculated to be (NOT RELATED) 
Select and explain. 
A. +4.07 mV, B. -4.07 mV, C. +71.7 mV, D. -71.7 mV
D: -71.7 mV
Answer: D: -71.7 mV 
Explanation: Nernst equation Ei - Eo = 61/-1 x log10 120/8 = -61 x 1.176 = -71.7 mV inside the cell. Note that for Cl-, the value for z (valence) is -1