Oxygen was not selected as the standard reference for atomic mass. Instead, the choice of the standard reference for atomic mass is based on the carbon-12 isotope.
The atomic mass unit (amu) is a unit of mass used to express atomic and molecular weights. The scale is based on the mass of the carbon-12 isotope, which is defined as exactly 12 amu. This choice was made because carbon is a common element found in organic compounds, and it has two stable isotopes, carbon-12 and carbon-13. Carbon-12 was selected as the standard because it is the most abundant isotope of carbon.
The choice of carbon-12 as the standard reference for atomic mass allows scientists to compare the masses of different atoms and molecules. For example, the atomic mass of oxygen is approximately 16 amu, meaning an oxygen atom is 16 times heavier than a carbon-12 atom. This comparison helps in calculating molecular masses, determining the composition of compounds, and understanding the stoichiometry of chemical reactions.
It's worth noting that oxygen does play an important role in other aspects of chemistry and physics, but it is not directly used as the standard reference for atomic mass.