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
The chief gas that is formed during decomposition is: 
Select and explain. 
A. H2S, B. Methane, C. Ammonia, D. Ethane
A: H2S
Answer: A: H2S 
Explanation: Ans. (A).H2 SEffects of Gas formation In putrefactionHydrogen sulphide, CO2 , ammonia, methane, mercaptans.Gas bubbles cause crepitations.Postmortem purge - Oozing of blood from nostrils & mouth.Gas stiffeningUterus & anus prolapse.Face bloatingPm blisters