Most reliable indicator to prevent oesophageal intubation?

Most reliable indicator to prevent
oesophageal intubation ?
a) Oxygen saturation on pulse oximeter
b) Measurement of CO2 in exhaled air (Etco2)
c) Direct visualization of passing tube beneath vocal cords
d) Auscultation over chest
Correct Answer - B
Ans, B. Measurement of CO2 in exhaled air (Etco2)