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
Least diffusible ion among following ? 
Select and explain. 
A. Na', B. K+, C. Cl-, D. Urea
A: Na'
Answer: A: Na' 
Explanation: 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.