This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Anaesthesia
Local anaesthetic with maximum ionized form at physiological pH 
Select and explain. 
A. Lignocaine, B. Etidocaine, C. Bupivacaine, D. Chloroprocaine
D: Chloroprocaine
Answer: D: Chloroprocaine 
Explanation: Local anaesthetics with pKa value closest at physiological pH (7.4) will have a higher concentration of nonionized (unionized) base. Thus, the agent with pKa value away from physiological pH will have more concentration of ionized formChloroprocaine has highest pKa value, hence maximum ionized form at physiological pH.(Refer: Morgan and Mikhail's Clinical Anaesthesiology, 5th edition, pg no.268-270)