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
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: Ans. is 'd' i.e., Chloroprocaine 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 form. Chloroprocaine has highest pKa value, hence maximum ionized form at physiological pH. Local anaesthetics with pKa value in increasing order Mepivacaine (7.6) < Etidocaine (7-7) < Lidocaine (7-8) Prilocaine (7.8) < Bupivacaine (8-1) = Ropivacaine (8-1) < Tetracaine (8.2) < Cocaine (8.7) < Procaine (8.9) < Chloroprocaine (9-0)