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: Anaesthesia
Capnography is useful for – 
Select and explain. 
A. Determining Vaporizer malfunction or contamination, B. Determining circuit hypoxia, C. Determining the appropriate placement of endotracheal tube, D. Detecting concentration of oxygen in the anesthetic circuit.
C: Determining the appropriate placement of endotracheal tube
Answer: C: Determining the appropriate placement of endotracheal tube 
Explanation: Uses of Capnography

It is the surest confirmatory sign of correct intubation in the trachea. Incorrect position of the tube in oesophagus instead of the trachea (oesophagal intubation) will yield ETCO2 = 0.
Intraoperative displacement of endotracheal tube → ETCO2 will become zero.
Obstruction or disconnections of endotracheal tube → ETCO2 will fall.
Diagnosing malignant hyperthermia → ETCO2 increases significantly (more than 100 mg Hg).