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
Excitable tissue at rest is least permeable to: 
Select and explain. 
A. Na., B. K', C. Ca", D. Cl
A: Na.
Answer: A: Na. 
Explanation: A i.e. Na'Order of permeability in excitable tissue at rest: K+ > Cl- > Na+Q