This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Toxicology, Subject name: Forensic Medicine
[{'content': 'Amyl nitrate is used as an antidote in which poisoning? \nSelect and explain. \nA. Arsenic poisoning, B. Hydrocyanide poisoning, C. Lead poisoning, D. Yellow poisoning', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Hydrocyanide poisoning * Amyl nitrite is used as an antidote in poisoning of hydrocyanic acid (cyanide).* Nitrates generate methaemoglobin which has high affinity for cyanide and forms cyanmethaemoglobin.* Cyanmethaemoglobin may again dissociate to release cyanide, therefore, sodium thiosulfate is given to form sod. thiocyanate which is poorly dissociable and is excreted in urine.", 'role': 'assistant'}]