This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Environment and Health, Subject name: Social & Preventive Medicine
Which of the following is used for room sterilization? 
Select and explain. 
A. Formaldehyde, B. Iodine, C. Lime, D. Ethylene oxide
A: Formaldehyde
Answer: A: Formaldehyde 
Explanation: Ans: a (Formaldehyde) Ref: Park, 19th ed, p. 110For room sterilization disinfectants used are:* Chlorine preparations that leave 25 ppm or more chlorine* Formaldehyde at 1 % or more* Phenolic disinfectants e.g., cresol 2.5%All these have a contact period of 4 hours before final washing. When fumigation is required gas most commonly used is formaldehyde. The room is kept closed for 6-12 hours to allow disinfection.Ethylene oxide: Heat sensitive articles may be sterilized at 55-60degC by ethylene oxide which kills bacteria, spores (tetanus spores) and also viruses.Descending order of resistance to sterilization is:PrionsBacterial sporeMycobacteriumNon lipid or small virusesFungiVegetative bacteriaLipid or medium size viruses* Most resistant to sterilization is prions (AIPGMEE 08).* Least resistant to sterilization is lipid or medium size viruses.