Oxygen-16 is the right answer as this isotope is not used in any type of radioactive dating, instead the oxygen isotopes are used for determening the processes in the living organisms.
Carbon-14 is not correct because it is one of the most commonly used isotopes for radioactive dating, being the most precise to a certain point of age.
Uranium-235 is not correct because it is an isotope commonly used for rafdioactive dating, especially for much longer periods.
Potassium-40 is not correct because in combination with argon-40 it is one of the main isotopes for determening the age through radioactive dating.
Changes in the pressure create the flow of the air to move up and down in the ear and thus create popping sound.
Explanation:
The ear-popping is caused by the phenomenon of the opening of the Eustachian tube when one swallows and it might be automatically when you blow our nose or are setting in an airplane and this sound is created when the air enters the middle ear through the tube.
