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Why was carbon-12 selected as the standard element for atomic mass?

Why was carbon-12 selected as the standard element for atomic mass?

Many of the people may be wondering why c-12 is taken as the standard element for atomic mass. If you are one of them than you are on the right platform to make your confusion clear. So, why c-12 only ???
At the very first period c-12 was not used as the standard element but Oxygen 16 were used at that time . Later than H-1(Hydrogen-1) was used as the standard element but according to the change in time the standard element was also change and c-12 came in used since that time till now.So let’s go deep into the history , the reason to choose c-12 as standard element is that the chemical atomic weights based on c-12 are almost identical to the chemical atomic weights based on the natural mix of oxygen.
The reason why c-12 is used is simple and logical. If we see carefully the mas of the H-1 element is nearly about 1.0078254u “u” being the atomic mass unit(a.m.u). But if we talk about the mass of c-12 element it is almost exactly 12.000000u so , the 1/12  mass of c-12 isotope will be exactly 1u.  But in the case of H-1 it won’t be as its mass is not exactly 1u  but it is 1.0078254u. As the decimal part many not bring so big problem in small and light elements but it bring huge problem in result of the heavy element and hefty(heavy and large) calculations. So IUPAC(International Union of Pure and Applied Chemistry) decided to make the c-12 as standard element because in order to standardize the result and make the calculation more accurate and because of above other reasons.
In short we can also say that once upon a time H-1 was also used as standard element but because of the inaccuracy that may occur because of hydrogen low mass and was disregarded. Before that O-16 was also used once. But it was given that oxygen 17 and 18 are also abundant(“existing or available in large quantities; plentiful”) so they were also disregarded.  But in 1960s c-12 was chosen because of it’s the quality of being logical and consistent to Avogadro’s Principle . Before scientist were heard to fight for standard element but it’s stability and abundance  it was basically to stop everybody from the fighting.  C-12 more accurately defines a mass for hydrogen and it’s unbounded in it’s ground state.
Source:- Quora

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