This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': "Least diffusible ion among following ? \nSelect and explain. \nA. Na', B. K+, C. Cl-, D. Urea", 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is'a'i.e., Na+Permeability coefficient & permeability of some impoant molecules in increasing order of frequency are Na+< K+< Cl- < Glucose < Tryptophan < Urea = Glycerol< Indole < H2O.", 'role': 'assistant'}]