This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Preoperative assessment and monitoring in anaesthesia, Subject name: Anaesthesia
Modern monitors to measure ETCO2 make Use of- 
Select and explain. 
A. Infrared absorption spectroscopy, B. Ultra violet rays, C. Laser technology, D. Scatter technology
A: Infrared absorption spectroscopy
Answer: A: Infrared absorption spectroscopy 
Explanation: Capnograpghy works on the priniciple of absorption spectrophotometry(CO2 absorbs infrared rays at a wavelength of 4280 nm)