This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Poisoning, Subject name: Forensic Medicine
Buonian line is seen with poisoning of - 
Select and explain. 
A. Mercury, B. Lead, C. Arsenic, D. Zinc
B: Lead
Answer: B: Lead 
Explanation: * Lead line (Buonian line) - a bluish line is present on gums. The line formation is due to lead sulphide. Lead sulphide is formed due to action of hydrogen sulphide gas, liberated from the decomposed food in the mouth, with lead. Ref: K.S.Narayan Reddy's Synopsis of Forensic Medicine and Toxicology, 29th edition, Chapter 26, page-300.