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
Cherry red colours of mucous membranes are seen in which of the following poisons: 
Select and explain. 
A. Carbon-monoxide, B. Carbon-dioxide, C. Hydrogen-sulphide, D. Chlorine
A: Carbon-monoxide
Answer: A: Carbon-monoxide 
Explanation: (Carbon - monoxide): Ref: 10.71 -PCARBON - MONOXIDE - is a colourless, odourless, non - irritant gas which cannot be perceived by the senses* The colour of skin, especially in areas of postmartem staining and in fair skinned persons. In bright cherry red if saturation is Co in blood exceeds about 30%.* Internally blood tissue and viscera are of a bright cherry red colour if there is more than 5 gms Co Hb/100 ml of blood