Question

Question 7

Why was carbon-12 preferred over oxygen-16 to be chosen as the standard reference for measuring atomic masses?

Answer 1

Oxygen is a mixture of O-16, O-17 and O-18 isotopes, which gives the average mass if oxygen is taken as the standard. C-12 is the most abundant isotope of carbon which constitutes 98.9% of available isotopes of carbon. So it was better to choose Carbon-12 isotopes as the standard.