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
Most diffusable ion in excitable tissue is - 
Select and explain. 
A. Na+, B. K+, C. PO4-, D. Cl-
B: K+
Answer: B: K+ 
Explanation: Points to note
Concentration of ions

Na+ concentration higher in ECF 
K+ concentration higher in ICF 
Cl- concentration higher in ECF
K+ leak channels allow K+ to move from ICF to ECF
Na+ is prevented from entering the cell.
Thus diffusion is highest for K+, then Cl- and least for Na+, when the cell is at rest.