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: Anaesthesia
All except one can cross blood brain barrier 
Select and explain. 
A. Neostigmine, B. Atropine, C. Lignocaine, D. Physostigmine
A: Neostigmine
Answer: A: Neostigmine 
Explanation: Neostigmine being quaternary amine , is highly ionised and does not cross blood brain barrier.