This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Neuromuscular Blocker, Subject name: Anaesthesia
Which of the following muscle relaxant causes pain on injection. 
Select and explain. 
A. Vecuronium, B. Pancuronium, C. Rocuronium, D. Succinylcholine
C: Rocuronium
Answer: C: Rocuronium 
Explanation: Most of the patients who received rocuronium before loss of consciousness after induction with barbiturates or other drugs complained of severe burning pain in their vein and arm. Rocuronium is supplied in a sterile, nonpyrogenic, isotonic solution. The isotonicity is obtained using sodium chloride, and the pH of 4 is achieved by adding acetic acid or sodium hydroxide . The pain can be decreased by prior administration of intravenous lidocaine. Rocuronium produces a burning pain in the vein or arm if administered before the loss of consciousness after induction of anesthesia. Prior administration of lidocaine may reduce the pain. Otherwise, rocuronium should be administered after induction of anesthesia and loss of consciousness.