This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Forensic Medicine
Gastric lavage turns black in presence of Silver nitrate, most probable poisoning was - 
Select and explain. 
A. Celphos, B. Malathion, C. Organophosphorus, D. Parathion
A: Celphos
Answer: A: Celphos 
Explanation: Gastric lavage fluid gives black colour in presence of silver nitrate because of reaction of posphine with silver nitrate.