Question

why oxygen was considered irrelevant for atomic mass.

full explanation .​

Answer 1

Firstly, Hydrogen was taken as standard whose mass was hypothetically 1 amu.

Later, it was replaced by O 16 atom as most of the elementary obtained fractional atomic mass with comparison to Hydrogen atom.

However, O16 was also removed due to contradiction between chemists and physicists for using O 16 or O 18 elements.

Finally, scientists took C 12 as the standard element for atomic mass.

Answer 2

Question:-

why oxygen was considered irrelevant for atomic mass.

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The reasons were :

(i) It reacted with large number of elements and formed compounds.

(ii) The atomic mass unit gave masses of most of the elements as whole numbers.

Carbon 12 was chosen because the chemical atomic weights based on C12 are almost identical to the chemical atomic weights based on the natural mix of oxygen.

hope it helps you..