<prompt> Blue line on gums seen in which poisoning?ZincMercuryPhenolOxalic acid  <response>: 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. 