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
Blue line on gums seen in which poisoning? 
Select and explain. 
A. Zinc, B. Mercury, C. Phenol, D. Oxalic acid
B: Mercury
Answer: B: Mercury 
Explanation: Ans. is 'b' i.e., Mercury * Burtonian line is blue line, which is seen on upper gums in lead poisoning.* Similar blue line (but not called burtonian line in these cases) is also seen in poisoning with Mercury (Hg), Copper (Cu), Silver (Ag), bismuth (Bi), and Iron (Fe).