Question

The average atomic mass of oxygen is 15.9994 amu. The atomic masses of its three isotopes are as follows:

O-16: 15.995 amu
O-17: 16.999 amu
O-18: 17.999 amu

Which isotope is most likely to have the greatest abundance in nature?

Answer 1

Oxygen-16 is the most abundant oxygen isotope as it is closest to the average mass of oxygen.

Answer 2

The average atomic mass of oxygen is the sum of the product of the atomic masses of the isotopes and their percentage abundance. The value of the average atomic mass is nearest to the atomic mass of O-16. Thus, the most abundant isotope should be O-16.